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  • Title: Spontaneous reverse movement of mRNA-bound tRNA through the ribosome.
    Author: Konevega AL, Fischer N, Semenkov YP, Stark H, Wintermeyer W, Rodnina MV.
    Journal: Nat Struct Mol Biol; 2007 Apr; 14(4):318-24. PubMed ID: 17369838.
    Abstract:
    During the translocation step of protein synthesis, a complex of two transfer RNAs bound to messenger RNA (tRNA-mRNA) moves through the ribosome. The reaction is promoted by an elongation factor, called EF-G in bacteria, which, powered by GTP hydrolysis, induces an open, unlocked conformation of the ribosome that allows for spontaneous tRNA-mRNA movement. Here we show that, in the absence of EF-G, there is spontaneous backward movement, or retrotranslocation, of two tRNAs bound to mRNA. Retrotranslocation is driven by the gain in affinity when a cognate E-site tRNA moves into the P site, which compensates the affinity loss accompanying the movement of peptidyl-tRNA from the P to the A site. These results lend support to the diffusion model of tRNA movement during translocation. In the cell, tRNA movement is biased in the forward direction by EF-G, which acts as a Brownian ratchet and prevents backward movement.
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