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Elongation factors are a set of proteins that function at theribosome, duringprotein synthesis, to facilitatetranslational elongation from the formation of the first to the lastpeptide bond of a growingpolypeptide. Most common elongation factors in prokaryotes areEF-Tu,EF-Ts,EF-G.[1] Bacteria and eukaryotes use elongation factors that are largely homologous to each other, but with distinct structures and different research nomenclatures.[2]
Elongation is the most rapid step in translation.[3] Inbacteria, it proceeds at a rate of 15 to 20amino acids added per second (about 45-60 nucleotides per second).[citation needed] Ineukaryotes the rate is about two amino acids per second (about 6 nucleotides read per second).[citation needed] Elongation factors play a role in orchestrating the events of this process, and in ensuring the high accuracy translation at these speeds.[citation needed]
| Bacterial | Eukaryotic/Archaeal | Function |
|---|---|---|
| EF-Tu | eEF-1A (α)[2] | mediates the entry of the aminoacyltRNA into a free site of theribosome.[4] |
| EF-Ts | eEF-1B (βγ)[2] | serves as the guaninenucleotide exchange factor for EF-Tu, catalyzing the release of GDP from EF-Tu.[2] |
| EF-G | eEF-2 | catalyzes the translocation of the tRNA and mRNA down the ribosome at the end of each round of polypeptide elongation. Causes large conformation changes.[5] |
| EF-P | eIF-5A | possibly stimulates formation of peptide bonds and resolves stalls.[6] |
| EF-4 | (None) | Proofreading |
| Note that EIF5A, the archaeal and eukaryotic homolog to EF-P, was named as an initiation factor but now considered an elongation factor as well.[6] | ||
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.[7][8] In humans, they includeTUFM,TSFM,GFM1,GFM2,GUF1; the nominalrelease factorMTRFR may also play a role in elongation.[9]
In bacteria,selenocysteinyl-tRNA requires a special elongation factorSelB (P14081) related to EF-Tu. A few homologs are also found in archaea, but the functions are unknown.[10]
Elongation factors are targets for the toxins of some pathogens. For instance,Corynebacterium diphtheriae producesdiphtheria toxin, which alters protein function in the host by inactivating elongation factor (EF-2). This results in the pathology and symptoms associated withdiphtheria. Likewise,Pseudomonas aeruginosaexotoxin A inactivates EF-2.[11]