Differential degradation of the Escherichia coli polynucleotide phosphorylase mRNA.

The transcript covering pnp, the gene encoding polynucleotide phosphorylase, is processed by RNaseIII at the 5'-upstream site of the pnp gene. In the RNaseIII-deficient strain, three species of the unprocessed transcript with different lengths could be detected. In this study, the stability of each transcript was analyzed by SI nuclease protection assay. The results show that the half-lives of the unprocessed transcripts are 8 min, whereas the half-life of the processed transcript is 1.5 min. It is also shown that the 5' segment of the unprocessed transcripts is more stable than the middle or the 3' segment.