STATIONARY PHASE-SPECIFIC MESSENGER-RNAS IN ESCHERICHIA-COLI ARE POLYADENYLATED

Polyadenylation of Escherichia coli specific mRNAs has so far been stu died primarily during the exponential phase of growth. As part of an i nvestigation of the polyadenylation of E. coli mRNAs in different phys iological contexts, we studied mRNA polyadenylation in stationary phas e by preparing a cDNA library from stationary phase RNA using oligodeo xythymidylate primers and analyzing the nucleotide sequence of cDNA cl ones corresponding to the stationary phase-specific genes, rpoS bolA, and dps. The sites of polyadenylation were found to be primarily in th e 3'-untranslated region, either at the putative rho-independent trans cription termination site (dps) or at several different sites upstream of the putative rho-independent terminator. A few examples of polyade nylation within the coding regions were also found, suggesting that nu cleolytic degradation often preceded polyadenylation. In contrast to t he poly(A) tracts characteristic of exponentially growing cells, many of the uncoded poly(A) tracts associated with stationary phase mRNA we re interspersed with other nucleotide residues. The observation of pos t-transcriptional polyadenylation of specific stationary phase mRNAs i n E. coli, some of which are transcribed by the RNA polymerase associa ted with sigma(s), demonstrates that mRNA polyadenylation is not confi ned to the exponential phase of growth. (C) 1997 Academic Press.