RNase E is required for the maturation of ssrA RNA and normal ssrA RNA peptide-tagging activity

During recent studies of ribonucleolytic "degradosome" complexes of Escheri chia coil, we found that degradosomes contain certain RNAs as well as RNase E and other protein components. One of these RNAs is ssrA (for small stabl e RNA) RNA (also known as tm RNA or 10Sa RNA), which functions as both a tR NA and mRNA to tag the C-terminal ends of truncated proteins with a short p eptide and target them for degradation. Here, we show that mature 363-nt ss rA RNA is generated by RNase E cleavage at the CCA-3' terminus of a 457-nt ssrA RNA precursor and that interference with this cleavage in vivo leads t o accumulation of the precursor and blockage of SsrA-mediated proteolysis. These results demonstrate that RNase E is required to produce mature ssrA R NA and for normal ssrA RNA peptide-tagging activity. Our findings indicate that RNase E, an enzyme already known to have a central role in RNA process ing and decay in E. coil, also has the previously unsuspected ability to af fect protein degradation through its role in maturation of the 3' end of ss rA RNA.