THE RPSO MESSENGER-RNA OF ESCHERICHIA-COLI IS POLYADENYLATED AT MULTIPLE SITES RESULTING FROM ENDONUCLEOLYTIC PROCESSING AND EXONUCLEOLYTICDEGRADATION

The rpsO monocistronic messenger, encoding ribosomal protein S15, is d estabilized upon polyadenylation occurring at the hairpin structure of the transcription terminator t1. We report that mRNA fragments differ ing from the monocistronic transcript by their 3' termini are also pol yadenylated in the absence of polynucleotide phosphorylase and RNase I I. Some of these 3' extremities result from endonucleolytic cleavages by RNase E and RNase III and from exonucleolytic degradation. Most of these mRNA fragments are destabilized upon polyadenylation with the ex ception of the RNA species generated by RNase III, RNase E appears to reduce the amount of poly(A) added at the transcription terminator t1.