Translation Translocations

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Science  05 Sep 2008:
Vol. 321, Issue 5894, pp. 1272
DOI: 10.1126/science.321.5894.1272b

Ribosomes translate mRNA into protein with the help of GTPases: the elongation factors (EFs). In prokaryotes, as each mRNA codon is presented in the A site of the ribosome, EF-Tu loads a complementary, amino acid-bearing tRNA into the A site. After peptide bond formation, EF-G translocates the ribosome along the mRNA strand by three nucleotides, moving the tRNA (now carrying the nascent polypeptide chain) into the neighboring P site and bringing the next codon into the A site. The GTPase EF4/LepA was recently found to promote backward translocation of the ribosome along the mRNA strand, moving the tRNA from the P site back into the A site. This function may allow the ribosome to recover from forward translocations of the wrong number of nucleotides. Connell et al. have visualized EF4 in complex with a ribosome and associated tRNAs using single-particle cryo-electron microscopy (EM). Fitting the crystal structure of EF4 into the cryo-EM reconstruction revealed that its C-terminal domain forms multiple contacts with a tRNA in the A site, suggesting that EF4 promotes back-translocation by stabilizing the A-site tRNA position over the P-site tRNA position. — NM*

Nat. Struct. Mol. Biol. 15, 10.1038/nsmb.1469 (2008).

  • *Nilah Monnier is a summer intern in Science's editorial department.

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