Elongation factors are a set of proteins that function at the
ribosome
Ribosomes ( ) are macromolecular machines, found within all cells, that perform biological protein synthesis (mRNA translation). Ribosomes link amino acids together in the order specified by the codons of messenger RNA (mRNA) molecules to fo ...
, during
protein synthesis
Protein biosynthesis (or protein synthesis) is a core biological process, occurring inside cells, balancing the loss of cellular proteins (via degradation or export) through the production of new proteins. Proteins perform a number of critical ...
, to facilitate
translational
Translation is the communication of the meaning of a source-language text by means of an equivalent target-language text. The English language draws a terminological distinction (which does not exist in every language) between ''transla ...
elongation from the formation of the first to the last
peptide bond
In organic chemistry, a peptide bond is an amide type of covalent chemical bond linking two consecutive alpha-amino acids from C1 (carbon number one) of one alpha-amino acid and N2 (nitrogen number two) of another, along a peptide or protein cha ...
of a growing
polypeptide
Peptides (, ) are short chains of amino acids linked by peptide bonds. Long chains of amino acids are called proteins. Chains of fewer than twenty amino acids are called oligopeptides, and include dipeptides, tripeptides, and tetrapeptides.
...
. Most common elongation factors in prokaryotes are
EF-Tu,
EF-Ts,
EF-G. Bacteria and eukaryotes use elongation factors that are largely homologous to each other, but with distinct structures and different research nomenclatures.
Elongation is the most rapid step in translation. 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 am ...
, it proceeds at a rate of 15 to 20
amino acids
Amino acids are organic compounds that contain both amino and carboxylic acid functional groups. Although hundreds of amino acids exist in nature, by far the most important are the alpha-amino acids, which comprise proteins. Only 22 alpha am ...
added per second (about 45-60 nucleotides per second). 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. Bacter ...
the rate is about two amino acids per second (about 6 nucleotides read per second). Elongation factors play a role in orchestrating the events of this process, and in ensuring the high accuracy translation at these speeds.
Nomenclature of homologous EFs
In addition to their cytoplasmic machinery, eukaryotic mitochondria and plastids have their own translation machinery, each with their own set of bacterial-type elongation factors.
In humans, they include
TUFM,
TSFM,
GFM1
Elongation factor G 1, mitochondrial is a protein that in humans is encoded by the ''GFM1'' gene. It is an EF-G homolog.
Eukaryotes contain two protein translational systems, one in the cytoplasm and one in the mitochondria. Mitochondrial transla ...
,
GFM2
Ribosome-releasing factor 2, mitochondrial is a protein that in humans is encoded by the ''GFM2'' gene.
Unlike the other EF-G
EF-G (elongation factor G, historically known as translocase) is a prokaryotic elongation factor involved in prot ...
,
GUF1
GUF1 homolog, GTPase is a protein that in humans is encoded by the GUF1 gene
In biology, the word gene (from , ; "...Wilhelm Johannsen coined the word gene to describe the Mendelian units of heredity..." meaning ''generation'' or ''birth ...
; the nominal
release factor
A release factor is a protein that allows for the termination of translation by recognizing the termination codon or stop codon in an mRNA sequence. They are named so because they release new peptides from the ribosome.
Background
During t ...
MTRFR may also play a role in elongation.
In bacteria,
selenocysteinyl-tRNA requires a special elongation factor ''SelB'' () related to EF-Tu. A few homologs are also found in archaea, but the functions are unknown.
As a target
Elongation factors are targets for the toxins of some pathogens. For instance, ''
Corynebacterium diphtheriae
''Corynebacterium diphtheriae'' is the pathogenic bacterium that causes diphtheria. It is also known as the Klebs–Löffler bacillus, because it was discovered in 1884 by German bacteriologists Edwin Klebs (1834–1912) and Friedrich Löff ...
'' produces
diphtheria toxin
Diphtheria toxin is an exotoxin secreted by ''Corynebacterium diphtheriae'', the pathogenic bacterium that causes diphtheria. The toxin gene is encoded by a prophageA prophage is a virus that has inserted itself into the genome of the h ...
, which alters protein function in the host by inactivating elongation factor (EF-2). This results in the pathology and symptoms associated with
Diphtheria
Diphtheria is an infection caused by the bacterium '' Corynebacterium diphtheriae''. Most infections are asymptomatic or have a mild clinical course, but in some outbreaks more than 10% of those diagnosed with the disease may die. Signs and s ...
. Likewise, ''
Pseudomonas aeruginosa
''Pseudomonas aeruginosa'' is a common encapsulated, gram-negative, aerobic– facultatively anaerobic, rod-shaped bacterium that can cause disease in plants and animals, including humans. A species of considerable medical importance, ''P. a ...
''
exotoxin A inactivates EF-2.
References
Further reading
*Alberts, B. et al. (2002). ''Molecular Biology of the Cell'', 4th ed. New York: Garland Science. .
*Berg, J. M. et al. (2002). ''Biochemistry'', 5th ed. New York: W.H. Freeman and Company. .
*Singh, B. D. (2002). ''Fundamentals of Genetics'', New Delhi, India: Kalyani Publishers. .
External links
nobelprize.orgExplaining the function of eukaryotic elongation factors
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{{GTPases
Protein biosynthesis