Elongation factors are a set of proteins that function at the
ribosome, during
protein synthesis, to facilitate
translational elongation from the formation of the first to the last
peptide bond of a growing
polypeptide. Most common elongation factors in prokaryotes are
EF-Tu
EF-Tu (elongation factor thermo unstable) is a prokaryotic elongation factor responsible for catalyzing the binding of an aminoacyl-tRNA (aa-tRNA) to the ribosome. It is a G-protein, and facilitates the selection and binding of an aa-tRNA to t ...
,
EF-Ts
EF-Ts (elongation factor thermo stable) is one of the prokaryotic elongation factors. It is found in human mitochrondria as TSFM. It is similar to eukaryotic EF-1B.
EF-Ts serves as the guanine nucleotide exchange factor for EF-Tu (elongatio ...
,
EF-G
EF-G (elongation factor G, historically known as translocase) is a prokaryotic elongation factor involved in protein translation. As a GTPase, EF-G catalyzes the movement (translocation) of transfer RNA (tRNA) and messenger RNA (mRNA) through t ...
. 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 Cell (biology), biological cell. They constitute a large domain (biology), domain of prokaryotic microorganisms. Typically a few micrometr ...
, it proceeds at a rate of 15 to 20
amino acids added per second (about 45-60 nucleotides per second). In
eukaryotes 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
Elongation factor Tu, mitochondrial is a protein that in humans is encoded by the ''TUFM'' gene
In biology, the word gene (from , ; "...Wilhelm Johannsen coined the word gene to describe the Mendelian units of heredity..." meaning ''gener ...
,
TSFM
Elongation factor Ts, mitochondrial is a protein that in humans is encoded by the ''TSFM'' gene. It is an EF-Ts
EF-Ts (elongation factor thermo stable) is one of the prokaryotic elongation factors. It is found in human mitochrondria as 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 translat ...
,
GFM2
Ribosome-releasing factor 2, mitochondrial is a protein that in humans is encoded by the ''GFM2'' gene.
Unlike the other EF-G homolog GFM1, GFM2 functions as a Ribosome Recycling Factor
Ribosome recycling factor or ribosome release factor (RRF ...
,
GUF1
GUF1 homolog, GTPase is a protein that in humans is encoded by the GUF1 gene.
It is the mitochondrial homolog of elongation factor 4
Elongation factor 4 (EF-4) is an elongation factor that is thought to back-Protein targeting, translocate o ...
; the nominal
release factor 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'' 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 host ...
, 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. aerug ...
''
exotoxin A
The Pseudomonas exotoxin (or exotoxin A) is an exotoxin produced by ''Pseudomonas aeruginosa''. ''Vibrio cholerae'' produces a similar protein called the Cholix toxin ().
It inhibits elongation factor-2. It does so by ADP-ribosylation of EF2 u ...
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