Polypeptide chain termination in vitro: isolation of a release factor.

The growing polypeptide chain remains bound to the ribosome-messenger RNA complex through the sRNA carrying the last amino acid incorporated into the polypeptide chain.' On completion of the polypeptide chain a mechanism must exist for releasing it from the protein-synthesizing machinery. To date, most of the effort has been concentrated on establishing the coded information required for this event.2-5 Very little is known about the biochemical mechanism of releasing the finished protein. The chain-terminating codon has to be read and the last peptidyl-sRNA bond must be cleaved. What components are required for this process remains to be determined.