Role of a Peptide Tagging System in Degradation of Proteins Synthesized from Damaged Messenger RNA

Variants of λ repressor and cytochrome b 562 translated from messenger RNAs without stop codons were modified by carboxyl terminal addition of an ssrA -encoded peptide tag and subsequently degraded by carboxyl terminal-specific proteases present in both the cytoplasm and periplasm of Escherichia coli . The tag appears to be added to the carboxyl terminus of the nascent polypeptide chain by cotranslational switching of the ribosome from the damaged messenger RNA to ssrA RNA.