Elongation factors are a set of proteins that function at the
ribosome
Ribosomes () are molecular machine, macromolecular machines, found within all cell (biology), cells, that perform Translation (biology), biological protein synthesis (messenger RNA translation). Ribosomes link amino acids together in the order s ...
, 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 critica ...
, to facilitate
translational 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. A polypeptide is a longer, continuous, unbranched peptide chain. Polypeptides that have a molecular mass of 10,000 Da or more are called proteins. Chains of fewer than twenty ...
. 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-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 (; : bacterium) are ubiquitous, mostly free-living organisms often consisting of one Cell (biology), biological cell. They constitute a large domain (biology), domain of Prokaryote, prokaryotic microorganisms. Typically a few micr ...
, 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 over 500 amino acids exist in nature, by far the most important are the Proteinogenic amino acid, 22 α-amino acids incorporated into p ...
added per second (about 45-60 nucleotides per second). In
eukaryotes
The eukaryotes ( ) constitute the domain of Eukaryota or Eukarya, organisms whose cells have a membrane-bound nucleus. All animals, plants, fungi, seaweeds, and many unicellular organisms are eukaryotes. They constitute a major group of ...
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,
GFM2,
GUF1; the nominal
release factor
A release factor is a protein that allows for the termination of Translation (biology), 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.
...
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 a Gram-positive 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 ...
'' produces
diphtheria toxin
Diphtheria toxin is an exotoxin secreted mainly by '' Corynebacterium diphtheriae'' but also by ''Corynebacterium ulcerans'' and '' Corynebacterium pseudotuberculosis'', the pathogenic bacterium that causes diphtheria. The toxin gene is enco ...
, 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 bacteria, bacterium ''Corynebacterium diphtheriae''. Most infections are asymptomatic or have a mild Course (medicine), clinical course, but in some outbreaks, the mortality rate approaches 10%. Signs a ...
. Likewise, ''
Pseudomonas aeruginosa
''Pseudomonas aeruginosa'' is a common Bacterial capsule, encapsulated, Gram-negative bacteria, Gram-negative, Aerobic organism, aerobic–facultative anaerobe, facultatively anaerobic, Bacillus (shape), rod-shaped bacteria, bacterium that can c ...
''
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