Figure 4.

Translation termination and ribosome recycling. (1) A pre-termination complex is shown to contain a stop codon in the A site of the ribosome. Two possible pathways for subsequent steps are depicted. (2) The recruitment of an eRF1/eRF3•GTP complex to the ribosome in the first step of the termination pathway. (2*) An alternative possibility is that a noncognate aminoacyl transfer RNA (aa-tRNA) is recruited to the A site of the ribosome to continue the elongation stage of translation (stop codon readthrough). Potential sources of regulation for determining which pathway is followed are summarized in the box and described in more detail in the main text. (3) Following the recruitment of eRF1/eRF3•GTP to the ribosome, a number of steps are undertaken to complete translation termination and are described in detail in the main text. Briefly, these steps involve the release of eRF3•GDP, recruitment of ABCE1•ATP, and the release of the polypeptide chain. Finally, the 60S ribosomal subunit is dissociated by the hydrolysis of the ATP bound to ABCE1. As mentioned in the main text, the precise pathway of 40S subunit recycling following termination is poorly understood.