Polynucleotide phosphorylase is required for the rapid degradation of the RNase E-processed rpsO mRNA of Escherichia coli devoid of its 3' hairpin.

The monocistronic transcript of rpsO undergoes an endonucleolytic cleavage downstream of the coding sequence, which removes the hairpin of the transcription terminator and initiates the rapid degradation of the message. We demonstrate here that the two rne-dependent cleavages, on both sides of the transcription terminator, are catalysed by RNase E in vitro and that the RNase E-processed rpsO message is rapidly degraded by polynucleotide phosphorylase, while RNase II produces stable decay intermediates. Moreover, we show that RNase E cuts in vitro the coding sequence of the rpsO mRNA at several sites which are not detected in vivo.