Polyadenylation of Escherichia coli transcripts plays an integral role in regulating intracellular levels of polynucleotide phosphorylase and RNase E.

Polyadenylation in Escherichia coli has been implicated in the destabilization of a variety of transcripts. However, transiently increasing intracellular poly(A) levels has also been shown to stabilize the pnp and rne transcripts, leading to increased polynucleotide phosphorylase (PNPase) and RNase E levels respectively. Here, we show that the half-lives of both the pnp and rne transcripts are dependent on the intracellular level of polyadenylated transcripts. In addition, experiments using pnp-lacZ and rne-lacZ translational fusions demonstrate that the variations in transcript stability and protein levels arise from alterations in the autoregulation of both genes. Further support for this conclusion is provided by the fact that, in an rne mutant in which autoregulation is inactivated by deletion of most of the 5' untranslated region, variations in the level of polyadenylated transcripts no longer affect RNase E protein expression. Of even more interest is the fact that the presence of a functional degradosome is essential for RNase E to detect increased levels of poly(A). Thus, it appears that polyadenylation of transcripts in E. coli serves as a sensing mechanism by which the cell adjusts the levels of both RNase E and PNPase.