![T4 Bacteriophage](https://upload.wikimedia.org/wikipedia/commons/9/9a/T4_Bacteriophage.gif)
Escherichia virus T4 is a species of
bacteriophage
A bacteriophage (), also known informally as a ''phage'' (), is a duplodnaviria virus that infects and replicates within bacteria and archaea. The term was derived from "bacteria" and the Greek φαγεῖν ('), meaning "to devour". Bacteri ...
s that infect ''
Escherichia coli
''Escherichia coli'' (),Wells, J. C. (2000) Longman Pronunciation Dictionary. Harlow ngland Pearson Education Ltd. also known as ''E. coli'' (), is a Gram-negative, facultative anaerobic, rod-shaped, coliform bacterium of the genus ''Escher ...
'' bacteria. It is a double-stranded DNA virus in the subfamily ''
Tevenvirinae'' from the family
Myoviridae
''Myoviridae'' is a family of bacteriophages in the order ''Caudovirales''. Bacteria and archaea serve as natural hosts. There are 625 species in this family, assigned to eight subfamilies and 217 genera.
Subdivisions
The subfamily ''Tevenvirinae ...
. T4 is capable of undergoing only a
lytic lifecycle and not the
lysogenic lifecycle. The species was formerly named T-even bacteriophage, a name which also encompasses, among other strains (or isolates),
Enterobacteria phage T2
Enterobacteria phage T2 is a virus that infects and kills '' E. coli''. It is in the genus '' Tequatrovirus'', and the family ''Myoviridae''. Its genome consists of linear double-stranded DNA, with repeats at either end. The phage is covered b ...
,
Enterobacteria phage T4
Escherichia virus T4 is a species of bacteriophages that infect ''Escherichia coli'' bacteria. It is a double-stranded DNA virus in the subfamily '' Tevenvirinae'' from the family Myoviridae. T4 is capable of undergoing only a lytic lifecycle ...
and
Enterobacteria phage T6
Enterobacteria phage T6 is a bacteriophage strain that infects ''Escherichia coli'' bacteria. It was one bacteriophage that was used as a model system in the 1950s in exploring the methods viruses replicate, along with the other ''T-even bacterio ...
.
Use in research
Dating back to the 1940s and continuing today, T-even phages are considered the best studied model organisms.
Model organisms
A model organism (often shortened to model) is a non-human species that is extensively studied to understand particular biological phenomena, with the expectation that discoveries made in the model organism will provide insight into the working ...
are usually required to be simple with as few as five
genes
In biology, the word gene (from , ; "...Wilhelm Johannsen coined the word gene to describe the Mendelian units of heredity..." meaning ''generation'' or ''birth'' or ''gender'') can have several different meanings. The Mendelian gene is a ba ...
. Yet, T-even phages are in fact among the largest and highest complexity
virus
A virus is a submicroscopic infectious agent that replicates only inside the living cells of an organism. Viruses infect all life forms, from animals and plants to microorganisms, including bacteria and archaea.
Since Dmitri Ivanovsky's 1 ...
, in which these phage's
genetic information
A nucleic acid sequence is a succession of bases signified by a series of a set of five different letters that indicate the order of nucleotides forming alleles within a DNA (using GACT) or RNA (GACU) molecule. By convention, sequences are usua ...
is made up of around 300
genes
In biology, the word gene (from , ; "...Wilhelm Johannsen coined the word gene to describe the Mendelian units of heredity..." meaning ''generation'' or ''birth'' or ''gender'') can have several different meanings. The Mendelian gene is a ba ...
. Coincident with their complexity, T-even viruses were found to have the unusual base
hydroxymethylcytosine (HMC) in place of the nucleic acid base
cytosine
Cytosine () ( symbol C or Cyt) is one of the four nucleobases found in DNA and RNA, along with adenine, guanine, and thymine (uracil in RNA). It is a pyrimidine derivative, with a heterocyclic aromatic ring and two substituents attached (an am ...
.
Genome and structure
The T4 virus's double-stranded
DNA genome
In the fields of molecular biology and genetics, a genome is all the genetic information of an organism. It consists of nucleotide sequences of DNA (or RNA in RNA viruses). The nuclear genome includes protein-coding genes and non-coding ge ...
is about 169
kbp long
and encodes 289
proteins
Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residues. Proteins perform a vast array of functions within organisms, including catalysing metabolic reactions, DNA replication, respo ...
. The T4 genome is terminally redundant. Upon DNA replication, long multi-genome length concatemers are formed, perhaps by a rolling circle mechanism of replication.
When packaged, the concatemer is cut at unspecific positions of the same length, leading to several genomes that represent
circular permutation
In mathematics, and in particular in group theory, a cyclic permutation (or cycle) is a permutation of the elements of some set ''X'' which maps the elements of some subset ''S'' of ''X'' to each other in a cyclic fashion, while fixing (that is, ma ...
s of the original.
The T4 genome bears
eukaryote
Eukaryotes () are organisms whose cells have a nucleus. All animals, plants, fungi, and many unicellular organisms, are Eukaryotes. They belong to the group of organisms Eukaryota or Eukarya, which is one of the three domains of life. Bacte ...
-like
intron
An intron is any nucleotide sequence within a gene that is not expressed or operative in the final RNA product. The word ''intron'' is derived from the term ''intragenic region'', i.e. a region inside a gene."The notion of the cistron .e., gene. ...
sequences.
Translation
The
Shine-Dalgarno sequence GAGG dominates in virus T4 early genes, whereas the sequence GGAG is a target for the T4
endonuclease
Endonucleases are enzymes that cleave the phosphodiester bond within a polynucleotide chain. Some, such as deoxyribonuclease I, cut DNA relatively nonspecifically (without regard to sequence), while many, typically called restriction endonucleases ...
RegB that initiates the early mRNA degradation.
Virus particle structure
T4 is a relatively large virus, at approximately 90
nm wide and 200 nm long (most viruses range from 25 to 200 nm in length). The DNA genome is held in an
icosahedral
In geometry, an icosahedron ( or ) is a polyhedron with 20 faces. The name comes and . The plural can be either "icosahedra" () or "icosahedrons".
There are infinitely many non- similar shapes of icosahedra, some of them being more symmetrica ...
head, also known as a
capsid
A capsid is the protein shell of a virus, enclosing its genetic material. It consists of several oligomeric (repeating) structural subunits made of protein called protomers. The observable 3-dimensional morphological subunits, which may or may ...
. The T4's tail is hollow so that it can pass its
nucleic acid
Nucleic acids are biopolymers, macromolecules, essential to all known forms of life. They are composed of nucleotides, which are the monomers made of three components: a 5-carbon sugar, a phosphate group and a nitrogenous base. The two main cl ...
into the cell it is infecting after attachment. Myoviridae phages like T4 have complex contractile tail structures with a large number of proteins involved in the tail assembly and function.
The tail fibres are also important in recognizing host cell surface receptors, so they determine if a bacterium is within the virus's host range.
The structure of the 6 megadalton T4 baseplate that comprises 127 polypeptide chains of 13 different proteins (gene products 5, 5.4, 6, 7, 8, 9, 10, 11, 12, 25, 27, 48 and 53) has recently been described in atomic detail. An atomic model of the proximal region of the tail tube formed by gp54 and the main tube protein gp19 have also been created. The tape measure protein gp29 is present in the baseplate-tail tube complexes, but it could not be modeled.
During assembly of the bacteriophage (phage) T4
virion
A virus is a submicroscopic infectious agent that replicates only inside the living cells of an organism. Viruses infect all life forms, from animals and plants to microorganisms, including bacteria and archaea.
Since Dmitri Ivanovsky's ...
, the morphogenetic proteins encoded by the phage
gene
In biology, the word gene (from , ; "...Wilhelm Johannsen coined the word gene to describe the Mendelian units of heredity..." meaning ''generation'' or ''birth'' or ''gender'') can have several different meanings. The Mendelian gene is a ba ...
s interact with each other in a characteristic sequence. Maintaining an appropriate balance in the amounts of each of these proteins produced during viral infection appears to be critical for normal phage T4 morphogenesis.
Phage T4 encoded proteins that determine virion structure include major structural components, minor structural components and non-structural proteins that catalyze specific steps in the morphogenesis sequence.
Phage T4 morphogenesis is divided into three independent pathways: the head, the tail and the long tail fibres as detailed by Yap and Rossman.
Infection process
The T4 virus initiates an ''Escherichia coli''
infection
An infection is the invasion of tissues by pathogens, their multiplication, and the reaction of host tissues to the infectious agent and the toxins they produce. An infectious disease, also known as a transmissible disease or communicable dise ...
by binding OmpC
porin proteins and
lipopolysaccharide
Lipopolysaccharides (LPS) are large molecules consisting of a lipid and a polysaccharide that are bacterial toxins. They are composed of an O-antigen, an outer core, and an inner core all joined by a covalent bond, and are found in the outer m ...
(LPS) on the surface of ''E. coli'' cells with its long tail fibers (LTF).
A recognition signal is sent through the LTFs to the baseplate. This unravels the short tail fibers (STF) that bind irreversibly to the ''E. coli'' cell surface. The baseplate changes conformation and the tail sheath contracts, causing GP5 at the end of the tail tube to puncture the outer
membrane
A membrane is a selective barrier; it allows some things to pass through but stops others. Such things may be molecules, ions, or other small particles. Membranes can be generally classified into synthetic membranes and biological membranes. B ...
of the cell.
The
lysozyme
Lysozyme (EC 3.2.1.17, muramidase, ''N''-acetylmuramide glycanhydrolase; systematic name peptidoglycan ''N''-acetylmuramoylhydrolase) is an antimicrobial enzyme produced by animals that forms part of the innate immune system. It is a glycoside ...
domain of GP5 is activated and degrades the periplasmic
peptidoglycan
Peptidoglycan or murein is a unique large macromolecule, a polysaccharide, consisting of sugars and amino acids that forms a mesh-like peptidoglycan layer outside the plasma membrane, the rigid cell wall (murein sacculus) characteristic of most ...
layer. The remaining part of the membrane is degraded and then DNA from the head of the virus can travel through the tail tube and enter the ''E. coli'' cell.
In 1952, Hershey and Chase
provided key evidence that the phage DNA, as distinct from protein, enters the host bacterial cell upon infection and is thus the genetic material of the phage. This finding suggested that DNA is, in general, the genetic material of different organisms.
Reproduction
The
lytic lifecycle (from entering a bacterium to its destruction) takes approximately 30 minutes (at 37 °C). Virulent bacteriophages multiply in their bacterial host immediately after entry. After the number of progeny phages reach a certain amount, they cause the host to lyse or break down, therefore they would be released and infect new host cells. The process of host lyses and release is called the
lytic cycle
The lytic cycle ( ) is one of the two cycles of viral reproduction (referring to bacterial viruses or bacteriophages), the other being the lysogenic cycle. The lytic cycle results in the destruction of the infected cell and its membrane. Bacter ...
. Lytic cycle is a cycle of viral reproduction that involves the destruction of the infected cell and its membrane. This cycle involves a virus that overtakes the host cell and its machinery to reproduce. Therefore, the virus must go through 5 stages in order to reproduce and infect the host cell:
*
Adsorption
Adsorption is the adhesion of atoms, ions or molecules from a gas, liquid or dissolved solid to a surface. This process creates a film of the ''adsorbate'' on the surface of the ''adsorbent''. This process differs from absorption, in which a f ...
and penetration (starting immediately)
* Arrest of host
gene expression
Gene expression is the process by which information from a gene is used in the synthesis of a functional gene product that enables it to produce end products, protein or non-coding RNA, and ultimately affect a phenotype, as the final effect. The ...
(starting immediately)
*
Enzyme
Enzymes () are proteins that act as biological catalysts by accelerating chemical reactions. The molecules upon which enzymes may act are called substrates, and the enzyme converts the substrates into different molecules known as products. A ...
synthesis (starting after 5 minutes)
*
DNA replication
In molecular biology, DNA replication is the biological process of producing two identical replicas of DNA from one original DNA molecule. DNA replication occurs in all living organisms acting as the most essential part for biological inheritanc ...
(starting after 10 minutes)
* Formation of new
virus
A virus is a submicroscopic infectious agent that replicates only inside the living cells of an organism. Viruses infect all life forms, from animals and plants to microorganisms, including bacteria and archaea.
Since Dmitri Ivanovsky's 1 ...
particles (starting after 12 minutes)
After the life cycle is complete, the host cell
bursts open and ejects the newly built viruses into the environment, destroying the host cell. T4 has a burst size of approximately 100-150 viral particles per infected host.
Benzer (1955 – 1959) developed a system for studying the fine structure of the gene using bacteriophage T4 mutants defective in the ''rIIA'' and ''rIIB'' genes.
The techniques employed were
complementation tests and crosses to detect
recombination, particularly between deletion mutations. These genetic experiments led to the finding of a unique linear order of mutational sites within the genes. This result provided strong evidence for the key idea that the gene has a linear structure equivalent to a length of DNA with many sites that can independently mutate.
Adsorption and penetration
![Phage injection](https://upload.wikimedia.org/wikipedia/commons/c/c5/Phage_injection.png)
Just like all other viruses, T-even phages don't just randomly attach to the surface of their host; instead they "search" and bind to
receptor
Receptor may refer to:
* Sensory receptor, in physiology, any structure which, on receiving environmental stimuli, produces an informative nerve impulse
*Receptor (biochemistry), in biochemistry, a protein molecule that receives and responds to a ...
s, specific
protein
Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residues. Proteins perform a vast array of functions within organisms, including catalysing metabolic reactions, DNA replication, respo ...
structures, found on the surface of the host. These receptors vary with the phage;
teichoic acid
Teichoic acids (''cf.'' Greek τεῖχος, ''teīkhos'', "wall", to be specific a fortification wall, as opposed to τοῖχος, ''toīkhos'', a regular wall) are bacterial copolymers of glycerol phosphate or ribitol phosphate and carbohydr ...
, cell wall proteins and
lipopolysaccharides
Lipopolysaccharides (LPS) are large molecules consisting of a lipid and a polysaccharide that are bacterial toxins. They are composed of an O-antigen, an outer core, and an inner core all joined by a covalent bond, and are found in the outer m ...
,
flagella
A flagellum (; ) is a hairlike appendage that protrudes from certain plant and animal sperm cells, and from a wide range of microorganisms to provide motility. Many protists with flagella are termed as flagellates.
A microorganism may have f ...
, and
pili all can serve as receptors for the phage to bind to. In order for the T-even phage to infect its host and begin its life cycle it must enter the first process of
infection
An infection is the invasion of tissues by pathogens, their multiplication, and the reaction of host tissues to the infectious agent and the toxins they produce. An infectious disease, also known as a transmissible disease or communicable dise ...
,
adsorption
Adsorption is the adhesion of atoms, ions or molecules from a gas, liquid or dissolved solid to a surface. This process creates a film of the ''adsorbate'' on the surface of the ''adsorbent''. This process differs from absorption, in which a f ...
of the phage to the bacterial cell. Adsorption is a value characteristic of phage-host pair and the adsorption of the phage on host cell surface is illustrated as a 2-stage process: reversible and irreversible. It involves the phages tail structure that begins when the phages tail fibers helps bind the phage to the appropriate receptor of its host. This process is reversible. One or more of the components of the base plate mediates irreversible process of binding of the phage to a bacterium.
Penetration is also a value characteristic of phage-host
infection
An infection is the invasion of tissues by pathogens, their multiplication, and the reaction of host tissues to the infectious agent and the toxins they produce. An infectious disease, also known as a transmissible disease or communicable dise ...
that involves the injection of the phages
genetic material
Nucleic acids are biopolymers, macromolecules, essential to all known forms of life. They are composed of nucleotides, which are the monomers made of three components: a 5-carbon sugar, a phosphate group and a nitrogenous base. The two main cla ...
inside the
bacterium
Bacteria (; singular: bacterium) are ubiquitous, mostly free-living organisms often consisting of one biological cell. They constitute a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria were among ...
. Penetration of
nucleic acid
Nucleic acids are biopolymers, macromolecules, essential to all known forms of life. They are composed of nucleotides, which are the monomers made of three components: a 5-carbon sugar, a phosphate group and a nitrogenous base. The two main cl ...
takes place after the irreversible adsorption phase. Mechanisms involving penetration of the phages nucleic acid are specific for each phage. This penetration mechanism can involve
electrochemical membrane potential,
ATP molecules, enzymatic splitting of
peptidoglycan
Peptidoglycan or murein is a unique large macromolecule, a polysaccharide, consisting of sugars and amino acids that forms a mesh-like peptidoglycan layer outside the plasma membrane, the rigid cell wall (murein sacculus) characteristic of most ...
layer, or all three of these factor can be vital for the penetration of the nucleic acid inside the bacterial cell. Studies have been done on the
T2 bacteriophage (T4-like phage) mechanism of penetration and it has shown that the phage's tail does not penetrate inside the bacterial cell wall and penetration of this phage involves electrochemical
membrane potential on the inner membrane.
Replication and packaging
Virus T4 genome is synthesized within the host cell using rolling circle replication.
[ The time it takes for DNA replication in a living cell was measured as the rate of virus T4 DNA elongation in virus-infected E. coli. During the period of exponential DNA increase at 37 °C, the rate was 749 nucleotides per second. The mutation rate per base pair per replication during virus T4 DNA synthesis is 1.7 per 10−8, a highly accurate DNA copying mechanism, with only 1 error in 300 copies. The virus also codes for unique ]DNA repair
DNA repair is a collection of processes by which a cell identifies and corrects damage to the DNA molecules that encode its genome. In human cells, both normal metabolic activities and environmental factors such as radiation can cause DNA dam ...
mechanisms.[Bernstein C. "Deoxyribonucleic acid repair in bacteriophage". Microbiol Rev. 1981 Mar;45(1):72-98. Review. ] The T4 phage head is assembled empty around a scaffolding protein, which is later degraded. Consequently, the DNA needs to enter the prohead through a tiny pore, which is achieved by a hexamer of gp17 interacting with DNA first, which also serves as a motor and nuclease. The T4 DNA packaging motor has been found to load DNA into virus capsids at a rate up to 2000 base pairs per second. The power involved, if scaled up in size, would be equivalent to that of an average automobile engine.
Release
The final step in viral reproduction and multiplication is determined by the release of virions from the host cell. The release of the virions occurs after the breakage of the bacterial plasma membrane. Nonenveloped viruses lyse the host cell which is characterized by viral proteins attacking the peptidoglycan or membrane. The lysis of the bacteria occurs when the capsids inside the cell release the enzyme lysozyme which break down the cell wall. The released bacteriophages infect other cells, and the viral multiplication cycle is repeated within those cells.
Multiplicity reactivation
Multiplicity reactivation (MR) is the process by which two or more virus genomes, each containing inactivating genome damage, can interact within an infected cell to form a viable virus genome. Salvador Luria
Salvador Edward Luria (August 13, 1912 – February 6, 1991) was an Italian microbiologist, later a Naturalized citizen of the United States#Naturalization, naturalized U.S. citizen. He won the Nobel Prize in Physiology or Medicine in 1969, with ...
, while studying UV irradiated virus T4 in 1946, discovered MR and proposed that the observed reactivation of damaged virus occurs by a recombination mechanism.(see refs.) This preceded the confirmation of DNA as the genetic material in 1952 in related virus T2 by the Hershey–Chase experiment
The Hershey–Chase experiments were a series of experiments conducted in 1952 by Alfred Hershey and Martha Chase that helped to confirm that DNA is genetic material.
While DNA had been known to biologists since 1869, many scientists still as ...
.[
As remembered by Luria (1984,][Salvador E. Luria. A Slot Machine, A Broken Test Tube: An Autobiography. Harper & Row, New York: 1984. Pp. 228. (USA and Canada)] pg. 97) the discovery of reactivation of irradiated virus (referred to as " multiplicity reactivation") immediately started a flurry of activity in the study of repair of radiation damage within the early phage group (reviewed by Bernstein[ in 1981). It turned out later that the repair of damaged virus by mutual help that Luria had discovered was only one special case of DNA repair. Cells of all types, not just, bacteria and their viruses, but all organisms studied, including humans, are now known to have complex biochemical processes for repairing DNA damages (see ]DNA repair
DNA repair is a collection of processes by which a cell identifies and corrects damage to the DNA molecules that encode its genome. In human cells, both normal metabolic activities and environmental factors such as radiation can cause DNA dam ...
). DNA repair processes are also now recognized as playing critical roles in protecting against aging
Ageing ( BE) or aging ( AE) is the process of becoming older. The term refers mainly to humans, many other animals, and fungi, whereas for example, bacteria, perennial plants and some simple animals are potentially biologically immortal. In ...
, cancer
Cancer is a group of diseases involving abnormal cell growth with the potential to invade or spread to other parts of the body. These contrast with benign tumors, which do not spread. Possible signs and symptoms include a lump, abnormal b ...
, and infertility
Infertility is the inability of a person, animal or plant to reproduce by natural means. It is usually not the natural state of a healthy adult, except notably among certain eusocial species (mostly haplodiploid insects). It is the normal state ...
.
MR is usually represented by "survival curves" where survival of plaque forming ability of multiply infected cells (multicomplexes) is plotted against dose of genome damaging agent. For comparison, the survival of virus plaque forming ability of singly infected cells (monocomplexes) is also plotted against dose of genome damaging agent. The top figure shows the survival curves for virus T4 multicomplexes and monocomplexes with increasing dose of UV light. Since survival is plotted on a log scale it is clear that survival of multicomplexes exceeds that of monocomplexes by very large factors (depending on dose). The UV inactivation curve for multicomplexes has an initial shoulder. Other virus T4 DNA damaging agents with shoulders in their multicomplex survival curves are X-rays and ethyl methane sulfonate (EMS).[ The presence of a shoulder has been interpreted to mean that two recombinational processes are used.] The first one repairs DNA with high efficiency (in the "shoulder"), but is saturated in its ability as damage increases; the second pathway functions at all levels of damage. Surviving T4 virus released from multicomplexes show no increase in mutation
In biology, a mutation is an alteration in the nucleic acid sequence of the genome of an organism, virus, or extrachromosomal DNA. Viral genomes contain either DNA or RNA. Mutations result from errors during DNA or viral replication, mi ...
, indicating that MR of UV irradiated virus is an accurate process.
The bottom figure shows the survival curves for inactivation of virus T4 by the DNA damaging agent mitomycin C
Mitomycin C is a mitomycin that is used as a chemotherapeutic agent by virtue of its antitumour activity.
Medical uses
It is given intravenously to treat upper gastro-intestinal cancers (e.g. esophageal carcinoma), anal cancers, and breast ...
(MMC). In this case the survival curve for multicomplexes has no initial shoulder, suggesting that only the second recombinational repair process described above is active. The efficiency of repair by this process is indicated by the observation that a dose of MMC that allows survival of only 1 in 1,000 monocomplexes allows survival of about 70% of multicomplexes. Similar multicomplex survival curves (without shoulders) were also obtained for the DNA damaging agents P32 decay, psoralen
Psoralen (also called psoralene) is the parent compound in a family of naturally occurring organic compounds known as the linear furanocoumarins. It is structurally related to coumarin by the addition of a fused furan ring, and may be considered ...
plus near-UV irradiation (PUVA), N-methyl-N'-nitro-N-nitrosoguanidine (MNNG), methyl methane sulfonate
Methyl methanesulfonate (MMS), also known as methyl mesylate, is an alkylating agent and a carcinogen. It is also a suspected reproductive toxicant, and may also be a skin/sense organ toxicant. It is used in cancer treatment.nitrous acid
Nitrous acid (molecular formula ) is a weak and monoprotic acid known only in Solution (chemistry), solution, in the gas phase and in the form of nitrite () salts. Nitrous acid is used to make diazonium salts from amines. The resulting diazoni ...
.[
Several of the genes found to be necessary for MR in virus T4 proved to be ]orthologs
Sequence homology is the biological homology between DNA, RNA, or protein sequences, defined in terms of shared ancestry in the evolutionary history of life. Two segments of DNA can have shared ancestry because of three phenomena: either a spec ...
for genes essential for recombination in prokaryote
A prokaryote () is a single-celled organism that lacks a nucleus and other membrane-bound organelles. The word ''prokaryote'' comes from the Greek πρό (, 'before') and κάρυον (, 'nut' or 'kernel').Campbell, N. "Biology:Concepts & Connec ...
s, eukaryote
Eukaryotes () are organisms whose cells have a nucleus. All animals, plants, fungi, and many unicellular organisms, are Eukaryotes. They belong to the group of organisms Eukaryota or Eukarya, which is one of the three domains of life. Bacte ...
s and archaea
Archaea ( ; singular archaeon ) is a domain of single-celled organisms. These microorganisms lack cell nuclei and are therefore prokaryotes. Archaea were initially classified as bacteria, receiving the name archaebacteria (in the Archaebac ...
. This includes, for instance, T4 gene ''uvsX'' which specifies a protein that has three-dimensional structural homology to RecA
RecA is a 38 kilodalton protein essential for the repair and maintenance of DNA. A RecA structural and functional homolog has been found in every species in which one has been seriously sought and serves as an archetype for this class of homolog ...
from ''Escherichia coli
''Escherichia coli'' (),Wells, J. C. (2000) Longman Pronunciation Dictionary. Harlow ngland Pearson Education Ltd. also known as ''E. coli'' (), is a Gram-negative, facultative anaerobic, rod-shaped, coliform bacterium of the genus ''Escher ...
'' and the homologous protein RAD51 in eukaryotes
Eukaryotes () are organisms whose cells have a nucleus. All animals, plants, fungi, and many unicellular organisms, are Eukaryotes. They belong to the group of organisms Eukaryota or Eukarya, which is one of the three domains of life. Bacte ...
and RadA in archaea
Archaea ( ; singular archaeon ) is a domain of single-celled organisms. These microorganisms lack cell nuclei and are therefore prokaryotes. Archaea were initially classified as bacteria, receiving the name archaebacteria (in the Archaebac ...
. It has been suggested that the efficient and accurate recombinational repair of DNA damages during MR may be analogous to the recombinational repair process that occurs during meiosis
Meiosis (; , since it is a reductional division) is a special type of cell division of germ cells in sexually-reproducing organisms that produces the gametes, such as sperm or egg cells. It involves two rounds of division that ultimately resu ...
in eukaryotes
Eukaryotes () are organisms whose cells have a nucleus. All animals, plants, fungi, and many unicellular organisms, are Eukaryotes. They belong to the group of organisms Eukaryota or Eukarya, which is one of the three domains of life. Bacte ...
.
History
Bacteriophages were first discovered by the English scientist Frederick Twort
Frederick William Twort FRS (22 October 1877 – 20 March 1950) was an English bacteriologist and was the original discoverer in 1915 of bacteriophages (viruses that infect bacteria). He studied medicine at St Thomas's Hospital, London, was super ...
in 1915 and Félix d'Hérelle
Félix d'Hérelle (25 April 1873 – 22 February 1949) was a French microbiologist. He was co-discoverer of bacteriophages (viruses that infect bacteria) and experimented with the possibility of phage therapy. D'Herelle has also been credited ...
in 1917. In the late 1930s, T. L. Rakieten proposed either a mixture of raw sewerage or a lysate from ''E. coli'' infected with raw sewerage to the two researchers Milislav Demerec and Ugo Fano
Ugo Fano (July 28, 1912 – February 13, 2001) was an Italian American physicist, notable for contributions to theoretical physics.
Biography
Ugo Fano was born into a wealthy Jewish family in Turin, Italy. His father was Gino Fano, a professo ...
. These two researchers isolated T3, T4, T5, and T6 from ''E.coli''. Also, in 1932, the researcher J. Bronfenbrenner had studied and worked on the T2 phage, at which the T2 phage was isolated from the virus. This isolation was made from a fecal material rather than from sewerage. At any rate, Max Delbrück
Max Ludwig Henning Delbrück (; September 4, 1906 – March 9, 1981) was a German–American biophysicist who participated in launching the molecular biology research program in the late 1930s. He stimulated physical science, physical scientist ...
was involved in the discovery of the T even phages. His part was naming the bacteriophages into Type 1(T1), Type 2 (T2), Type 3 (T3), etc.
The specific time and place of T4 virus isolation remains unclear, though they were likely found in sewage or fecal material. T4 and similar viruses were described in a paper by Thomas F. Anderson, Max Delbrück, and Milislav Demerec in November 1944.
In 1943, Salvador Luria
Salvador Edward Luria (August 13, 1912 – February 6, 1991) was an Italian microbiologist, later a Naturalized citizen of the United States#Naturalization, naturalized U.S. citizen. He won the Nobel Prize in Physiology or Medicine in 1969, with ...
and Delbrück showed that bacterial mutations
In biology, a mutation is an alteration in the nucleic acid sequence of the genome of an organism, virus, or extrachromosomal DNA. Viral genomes contain either DNA or RNA. Mutations result from errors during DNA or viral replication, mi ...
for phage resistance arise in the absence of selection
Selection may refer to:
Science
* Selection (biology), also called natural selection, selection in evolution
** Sex selection, in genetics
** Mate selection, in mating
** Sexual selection in humans, in human sexuality
** Human mating strateg ...
, rather than being a response to selection.[ The traditional wisdom among bacteriologists prior to 1943 was that bacteria had no chromosomes and no genes. The Luria–Delbrück experiment showed that bacteria, like other established model genetic organisms, have genes, and that these can spontaneously mutate to generate mutants that may then reproduce to form clonal lineages. That year, they also began working with ]Alfred Hershey
Alfred Day Hershey (December 4, 1908 – May 22, 1997) was an American Nobel Prize–winning bacteriologist and geneticist.
He was born in Owosso, Michigan and received his B.S. in chemistry at Michigan State University in 1930 and his Ph.D. ...
, another phage experimenter. (The three would share the 1969 Nobel Prize in Physiology or Medicine
The Nobel Prize in Physiology or Medicine is awarded yearly by the Nobel Assembly at the Karolinska Institute for outstanding discoveries in physiology or medicine. The Nobel Prize is not a single prize, but five separate prizes that, accord ...
, "for work on the replication mechanism and genetics of viruses".)
The phage group was an informal network of biologists centered on Max Delbrück that carried out basic research mainly on bacteriophage T4 and made numerous seminal contributions to microbial genetics
Microbial genetics is a subject area within microbiology and genetic engineering. Microbial genetics studies microorganisms for different purposes. The microorganisms that are observed are bacteria, and archaea. Some fungi and protozoa are also s ...
and the origins of molecular biology in the mid-20th century. In 1961, Sydney Brenner
Sydney Brenner (13 January 1927 – 5 April 2019) was a South African biologist. In 2002, he shared the Nobel Prize in Physiology or Medicine with H. Robert Horvitz and Sir John E. Sulston. Brenner made significant contributions to work ...
, an early member of the phage group, collaborated with Francis Crick
Francis Harry Compton Crick (8 June 1916 – 28 July 2004) was an English molecular biologist, biophysicist, and neuroscientist. He, James Watson, Rosalind Franklin, and Maurice Wilkins played crucial roles in deciphering the helical struc ...
, Leslie Barnett
Leslie Barnett (born 12 October 1920 as Margaret Leslie Collard – died 10 February 2002) was a British biologist who worked with Francis Crick, Sydney Brenner, and Richard J. Watts-Tobin to genetically demonstrate the genetic code, triplet na ...
and Richard Watts-Tobin at the Cavendish Laboratory in Cambridge to perform genetic experiments that demonstrated the basic nature of the genetic code
The genetic code is the set of rules used by living cells to translate information encoded within genetic material ( DNA or RNA sequences of nucleotide triplets, or codons) into proteins. Translation is accomplished by the ribosome, which links ...
for proteins. These experiments, carried out with mutants of the rIIB gene of phage T4, showed, that for a gene that encodes a protein, three sequential bases of the gene's DNA specify each successive amino acid of the protein. Thus the genetic code is a triplet code, where each triplet (called a codon) specifies a particular amino acid. They also obtained evidence that the codons do not overlap with each other in the DNA sequence encoding a protein, and that such a sequence is read from a fixed starting point.
During 1962-1964 phage T4 researchers provided an opportunity to study the function of virtually all of the genes that are essential for growth of the phage under laboratory conditions.[Edgar RS Conditional lethals: in Phage and the Origins of Molecular Biology (2007) Edited by John Cairns, Gunther S. Stent, and James D. Watson, Cold Spring Harbor Laboratory of Quantitative Biology, Cold Spring Harbor, Long Island, New York ] These studies were facilitated by the discovery of two classes of conditional lethal mutants. One class of such mutants is known as amber mutants. Another class of conditional lethal mutants is referred to as temperature-sensitive mutant
Temperature-sensitive mutants are variants of genes that allow normal function of the organism at low temperatures, but altered function at higher temperatures. Cold sensitive mutants are variants of genes that allow normal function of the organi ...
s Studies of these two classes of mutants led to considerable insight into numerous fundamental biologic problems. Thus understanding was gained on the functions and interactions of the proteins employed in the machinery of DNA replication
In molecular biology, DNA replication is the biological process of producing two identical replicas of DNA from one original DNA molecule. DNA replication occurs in all living organisms acting as the most essential part for biological inheritanc ...
, repair
The technical meaning of maintenance involves functional checks, servicing, repairing or replacing of necessary devices, equipment, machinery, building infrastructure, and supporting utilities in industrial, business, and residential installa ...
and recombination, and on how viruses are assembled from protein and nucleic acid components (molecular morphogenesis
Morphogenesis (from the Greek ''morphê'' shape and ''genesis'' creation, literally "the generation of form") is the biological process that causes a cell, tissue or organism to develop its shape. It is one of three fundamental aspects of devel ...
). Furthermore, the role of chain terminating codons was elucidated. One noteworthy study used amber mutants defective in the gene encoding the major head protein of phage T4. This experiment provided strong evidence for the widely held, but prior to 1964 still unproven, "sequence hypothesis" that the amino acid sequence
Protein primary structure is the linear sequence of amino acids in a peptide or protein. By convention, the primary structure of a protein is reported starting from the amino-terminal (N) end to the carboxyl-terminal (C) end. Protein biosynthe ...
of a protein is specified by the nucleotide sequence
A nucleic acid sequence is a succession of bases signified by a series of a set of five different letters that indicate the order of nucleotides forming alleles within a DNA (using GACT) or RNA (GACU) molecule. By convention, sequences are usu ...
of the gene
In biology, the word gene (from , ; "...Wilhelm Johannsen coined the word gene to describe the Mendelian units of heredity..." meaning ''generation'' or ''birth'' or ''gender'') can have several different meanings. The Mendelian gene is a ba ...
determining the protein. Thus, this study demonstrated the co-linearity of the gene with its encoded protein.
A number of Nobel Prize
The Nobel Prizes ( ; sv, Nobelpriset ; no, Nobelprisen ) are five separate prizes that, according to Alfred Nobel's will of 1895, are awarded to "those who, during the preceding year, have conferred the greatest benefit to humankind." Alfr ...
winners worked with virus T4 or T4-like viruses including Max Delbrück
Max Ludwig Henning Delbrück (; September 4, 1906 – March 9, 1981) was a German–American biophysicist who participated in launching the molecular biology research program in the late 1930s. He stimulated physical science, physical scientist ...
, Salvador Luria
Salvador Edward Luria (August 13, 1912 – February 6, 1991) was an Italian microbiologist, later a Naturalized citizen of the United States#Naturalization, naturalized U.S. citizen. He won the Nobel Prize in Physiology or Medicine in 1969, with ...
, Alfred Hershey
Alfred Day Hershey (December 4, 1908 – May 22, 1997) was an American Nobel Prize–winning bacteriologist and geneticist.
He was born in Owosso, Michigan and received his B.S. in chemistry at Michigan State University in 1930 and his Ph.D. ...
, James D. Watson
James Dewey Watson (born April 6, 1928) is an American molecular biologist, geneticist, and zoologist. In 1953, he co-authored with Francis Crick the academic paper proposing the double helix structure of the DNA molecule. Watson, Crick and ...
, and Francis Crick
Francis Harry Compton Crick (8 June 1916 – 28 July 2004) was an English molecular biologist, biophysicist, and neuroscientist. He, James Watson, Rosalind Franklin, and Maurice Wilkins played crucial roles in deciphering the helical struc ...
. Other important scientists who worked with virus T4 include Michael Rossmann
Michael G. Rossmann (30 July 1930 – 14 May 2019) was a German-American physicist, microbiologist, and Hanley Distinguished Professor of Biological Sciences at Purdue University who led a team of researchers to be the first to map the structure ...
, Seymour Benzer, Bruce Alberts
Bruce Michael Alberts (born April 14, 1938, in Chicago, Illinois) is an American biochemist and the Chancellor’s Leadership Chair in Biochemistry and Biophysics for Science and Education, Emeritus at the University of California, San Francis ...
, Gisela Mosig, Richard Lenski
Richard Eimer Lenski (born August 13, 1956) is an American evolutionary biologist, a Hannah Distinguished Professor of Microbial Ecology at Michigan State University. He is a member of the National Academy of Sciences and a MacArthur fellow. ...
, and James Bull.
See also
* T4 ''rII'' system
* T2 phage
Enterobacteria phage T2 is a virus that infects and kills '' E. coli''. It is in the genus '' Tequatrovirus'', and the family ''Myoviridae''. Its genome consists of linear double-stranded DNA, with repeats at either end. The phage is covered b ...
* T6 phage
* Bacteriophage
A bacteriophage (), also known informally as a ''phage'' (), is a duplodnaviria virus that infects and replicates within bacteria and archaea. The term was derived from "bacteria" and the Greek φαγεῖν ('), meaning "to devour". Bacteri ...
* Virology
Virology is the Scientific method, scientific study of biological viruses. It is a subfield of microbiology that focuses on their detection, structure, classification and evolution, their methods of infection and exploitation of host (biology), ...
References
Further reading
*
* Karam, J., Petrov, V., Nolan, J., Chin, D., Shatley, C., Krisch, H., and Letarov, A. The T4-like phages genome project
https://web.archive.org/web/20070523215704/http://phage.bioc.tulane.edu/
'' (The T4-like phage full genomic sequence depository)''
* Mosig, G., and F. Eiserling. 2006. T4 and related phages: structure and development, R. Calendar and S. T. Abedon (eds.), The Bacteriophages. Oxford University Press, Oxford. ''(Review of phage T4 biology)''
* ''(Indication of prevalence and T4-like phages in the wild)''
* ''(Characterization of a T4-like phage)''
*
* ''(Review of phage T4, from the perspective of its genome)''
* ''(Overview of the RB49 genome, a T4-like phage)''
* ''(T4 phage application in biotechnology for studying protein interaction)''
* ''(Indication of the prevalence of T4-type sequences in the wild)''
* ''(Historical description of the isolation of the T4-like phages T2, T4, and T6)''
* ''(Nearly complete list of then-known T4-like phages)''
* ''(Overview of various T4-like phages from the perspective of their genomes)''
* ''(Comparison of the genomes of various T4-like phages)''
* Karam, J. D. ''et al.'' 1994. Molecular Biology of Bacteriophage T4. ASM Press, Washington, DC. ''(The second T4 bible, go here, as well as Mosig and Eiserling, 2006, to begin to learn about the biology T4 phage)''
* Eddy, S. R. 1992. Introns in the T-Even Bacteriophages. PhD thesis. University of Colorado at Boulder. ''(Chapter 3 provides overview of various T4-like phages as well as the isolation of then-new T4-like phages)''
* Surdis, T.J "et al" UC Santa Cruz, Nov 1978, "Bacteriophage attachment methods specific to T4", analysis, Overview.
* Mathews, C. K., E. M. Kutter, G. Mosig, and P. B. Berget. 1983. Bacteriophage T4. American Society for Microbiology, Washington, DC. ''(The first T4 bible; not all information here is duplicated in Karam ''et al.'', 1994; see especially the introductory chapter by Doermann for a historical overview of the T4-like phages)''
* Russell, R. L. 1967. Speciation Among the T-Even Bacteriophages. PhD thesis. California Institute of Technology. ''(Isolation of the RB series of T4-like phages)''
* ''(rare type of translational regulation characterized in T4)''
* ''(T4-like phage isolation, including that of phage Ox2)''
External links
Animation of T4 Bacteriophage Infecting E.coli
Animation of T4 Bacteriophage DNA packaging
{{DEFAULTSORT:Enterobacteria Phage T4
Myoviridae