A bacterial artificial chromosome (BAC) is a
DNA construct A DNA construct is an artificially-designed segment of DNA borne on a vector that can be used to incorporate genetic material into a target tissue or cell. A DNA construct contains a DNA insert, called a transgene, delivered via a transformation v ...
, based on a functional fertility
plasmid
A plasmid is a small, extrachromosomal DNA molecule within a cell that is physically separated from chromosomal DNA and can replicate independently. They are most commonly found as small circular, double-stranded DNA molecules in bacteria; how ...
(or
F-plasmid
The fertility factor (first named F by one of its discoverers Esther Lederberg; also called the sex factor in '' E. coli'' or the F sex factor; also called F-plasmid) allows genes to be transferred from one bacterium carrying the factor to another ...
), used for
transforming and
cloning
Cloning is the process of producing individual organisms with identical or virtually identical DNA, either by natural or artificial means. In nature, some organisms produce clones through asexual reproduction. In the field of biotechnology, cl ...
in
bacteria
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 ...
, usually ''
E. 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 ...
''.
F-plasmids play a crucial role because they contain partition genes that promote the even distribution of plasmids after bacterial cell division. The bacterial artificial chromosome's usual insert size is 150–350
kbp.
A similar
cloning vector
A cloning vector is a small piece of DNA that can be stably maintained in an organism, and into which a foreign DNA fragment can be inserted for cloning purposes. The cloning vector may be DNA taken from a virus, the cell of a higher organism, or ...
called a
PAC has also been produced from the DNA of P1 bacteriophage.
BACs are often used to
sequence
In mathematics, a sequence is an enumerated collection of objects in which repetitions are allowed and order matters. Like a set, it contains members (also called ''elements'', or ''terms''). The number of elements (possibly infinite) is calle ...
the genome of organisms in
genome project
Genome projects are scientific endeavours that ultimately aim to determine the complete genome sequence of an organism (be it an animal, a plant, a fungus, a bacterium, an archaean, a protist or a virus) and to annotate protein-coding genes and ot ...
s, for example the
Human Genome Project
The Human Genome Project (HGP) was an international scientific research project with the goal of determining the base pairs that make up human DNA, and of identifying, mapping and sequencing all of the genes of the human genome from both a ...
. A short piece of the organism's
DNA is amplified as an insert in BACs, and then sequenced. Finally, the sequenced parts are rearranged ''
in silico
In biology and other experimental sciences, an ''in silico'' experiment is one performed on computer or via computer simulation. The phrase is pseudo-Latin for 'in silicon' (correct la, in silicio), referring to silicon in computer chips. It ...
'', resulting in the genomic sequence of the organism. BACs were replaced with faster and less laborious sequencing methods like whole genome
shotgun sequencing
In genetics, shotgun sequencing is a method used for sequencing random DNA strands. It is named by analogy with the rapidly expanding, quasi-random shot grouping of a shotgun.
The Sanger sequencing#Method, chain-termination method of DNA sequencin ...
and now more recently
next-gen sequencing
DNA sequencing is the process of determining the nucleic acid sequence – the order of nucleotides in DNA. It includes any method or technology that is used to determine the order of the four bases: adenine, guanine, cytosine, and thymine. The ...
.
Common gene components
;''repE'': for plasmid replication and regulation of copy number.
;''
parA
Para, or PARA, may refer to:
Businesses and organizations
* Paramount Global, traded as PARA on the Nasdaq stock exchange
* Para Group, the former name of CT Corp
* Para Rubber, now Skellerup, a New Zealand manufacturer
* Para USA, formerly ...
and
parB'': for partitioning F plasmid DNA to daughter cells during division and ensures stable maintenance of the BAC.
;A
selectable marker A selectable marker is a gene introduced into a cell, especially a bacterium or to cells in culture, that confers a trait suitable for artificial selection. They are a type of reporter gene used in laboratory microbiology, molecular biology, and gen ...
: for
antibiotic resistance
Antimicrobial resistance (AMR) occurs when microbes evolve mechanisms that protect them from the effects of antimicrobials. All classes of microbes can evolve resistance. Fungi evolve antifungal resistance. Viruses evolve antiviral resistance. ...
; some BACs also have
lacZ
The ''lactose'' operon (''lac'' operon) is an operon required for the transport and metabolism of lactose in ''E. coli'' and many other enteric bacteria. Although glucose is the preferred carbon source for most bacteria, the ''lac'' operon allows ...
at the cloning site for
blue/white selection.
;''T7 & Sp6'':
phage promoters for transcription of inserted genes.
Contribution to models of disease
Inherited disease
BACs are now being utilized to a greater extent in
modelling genetic diseases
A model is an informative representation of an object, person or system. The term originally denoted the Plan_(drawing), plans of a building in late 16th-century English, and derived via French and Italian ultimately from Latin ''modulus'', a mea ...
, often alongside
transgenic
A transgene is a gene that has been transferred naturally, or by any of a number of genetic engineering techniques, from one organism to another. The introduction of a transgene, in a process known as transgenesis, has the potential to change the ...
mice. BACs have been useful in this field as complex genes may have several regulatory sequences upstream of the encoding sequence, including various
promoter sequences that will govern a gene's expression level. BACs have been used to some degree of success with mice when studying neurological diseases such as Alzheimer's disease or as in the case of
aneuploidy
Aneuploidy is the presence of an abnormal number of chromosomes in a cell, for example a human cell having 45 or 47 chromosomes instead of the usual 46. It does not include a difference of one or more complete sets of chromosomes. A cell with any ...
associated with Down syndrome. There have also been instances when they have been used to study specific
oncogene
An oncogene is a gene that has the potential to cause cancer. In tumor cells, these genes are often mutated, or expressed at high levels. s associated with cancers. They are transferred over to these genetic disease models by electroporation/transformation, transfection with a suitable virus or microinjection. BACs can also be utilized to detect genes or large sequences of interest and then used to map them onto the human chromosome using BAC
arrays
An array is a systematic arrangement of similar objects, usually in rows and columns.
Things called an array include:
{{TOC right
Music
* In twelve-tone and serial composition, the presentation of simultaneous twelve-tone sets such that the ...
. BACs are preferred for these kind of genetic studies because they accommodate much larger sequences without the risk of rearrangement, and are therefore more stable than other types of cloning vectors.
Infectious disease
The genomes of several large
DNA viruses
A DNA virus is a virus that has a genome made of deoxyribonucleic acid (DNA) that is replicated by a DNA polymerase. They can be divided between those that have two strands of DNA in their genome, called double-stranded DNA (dsDNA) viruses, and ...
and
RNA viruses
''Orthornavirae'' is a kingdom of viruses that have genomes made of ribonucleic acid (RNA), those genomes encoding an RNA-dependent RNA polymerase (RdRp). The RdRp is used to transcribe the viral RNA genome into messenger RNA (mRNA) and to repli ...
have been cloned as BACs. These constructs are referred to as "infectious clones", as transfection of the BAC construct into host cells is sufficient to initiate viral infection. The infectious property of these BACs has made the study of many viruses such as the
herpesviruses,
poxviruses
''Poxviridae'' is a family of double-stranded DNA viruses. Vertebrates and arthropods serve as natural hosts. There are currently 83 species in this family, divided among 22 genera, which are divided into two subfamilies. Diseases associated wit ...
and
coronaviruses
Coronaviruses are a group of related RNA viruses that cause diseases in mammals and birds. In humans and birds, they cause respiratory tract infections that can range from mild to lethal. Mild illnesses in humans include some cases of the com ...
more accessible.
Molecular studies of these viruses can now be achieved using genetic approaches to mutate the BAC while it resides in bacteria. Such genetic approaches rely on either linear or circular targeting vectors to carry out
homologous recombination
Homologous recombination is a type of genetic recombination in which genetic information is exchanged between two similar or identical molecules of double-stranded or single-stranded nucleic acids (usually DNA as in cellular organisms but may ...
.
See also
*
Cosmid
A cosmid is a type of hybrid plasmid that contains a Lambda phage ''cos'' sequence. They are often used as a cloning vector in genetic engineering. Cosmids can be used to build genomic libraries. They were first described by Collins and Hohn in ...
*
End-sequence profiling
End-sequence profiling (ESP) (sometimes "Paired-end mapping (PEM)") is a method based on sequence-tagged connectors developed to facilitate ''de novo'' genome sequencing to identify high-resolution copy number and structural aberrations such as ...
*
Fosmid Fosmids are similar to cosmids but are based on the bacterial F-plasmid. The cloning vector is limited, as a host (usually '' E. coli'') can only contain one fosmid molecule. Fosmids can hold DNA inserts of up to 40 kb in size; often the source of t ...
*
Human artificial chromosome A human artificial chromosome (HAC) is a microchromosome that can act as a new chromosome in a population of human cells. That is, instead of 46 chromosomes, the cell could have 47 with the 47th being very small, roughly 6–10megabases (Mb) in size ...
*
Secondary chromosome Secondary chromosomes (recently renamed chromids) are a class of bacterial replicons (replicating DNA molecules). These replicons are called "chromids" because they have characteristic features of both ''chrom''osomes and plasm''id''s. Early on, ...
*
Yeast artificial chromosome
Yeast artificial chromosomes (YACs) are genetically engineered chromosomes derived from the DNA of the yeast, ''Saccharomyces cerevisiae'', which is then ligated into a bacterial plasmid. By inserting large fragments of DNA, from 100–1000 ...
References
External links
The Big Bad BAC: Bacterial Artificial Chromosomes— a review from the
Science Creative Quarterly
Empire Genomics(company that sells BAC clones from genomic libraries)
Amplicon Express(company that makes custom BAC libraries)
{{DEFAULTSORT:Bacterial Artificial Chromosome
Genomics techniques
Molecular biology techniques