The rpsO mRNA, encoding ribosomal protein S15, is only partly stabilized when the three ribonucleases implicated in its degradation-RNase E, polynucleotide phosphorylase, and RNase II-are inactivated. In the strain deficient for RNase E and 3'-to-5' exoribonucleases, degradation of this mRNA is correlated with the appearance of posttranscriptionally elongated molecules. We report that these elongated mRNAs harbor poly(A) tails, most of which are fused downstream of the 3'-terminal hairpin at the site where transcription terminates. Poly(A) tails are shorter in strains containing 3'-to-5' exoribonucleases. Inactivation of poly(A) polymerase I (pcnB) prevents polyadenylylation and stabilizes the rpsO mRNA if RNase E is inactive. In contrast polyadenylylation does not significantly modify the stability of rpsO mRNA undergoing RNase E-mediated degradation.
RNase III has been implicated in the control of gene expression by the processing of mRNA. We have found that the rnc operon is autoregulated; rnc‐ mutant strains oversynthesize the operon's mRNA and protein products. A site in the 5′‐noncoding region of the operon's message is cleaved by RNase III. This site‐specific cleavage appears to be the initial step in the functional inactivation of the message, since the half‐life of the cut message is dramatically shorter than that of the uncut message.
The transcripts covering pnp, the gene encoding polynucleotide phosphorylase, are processed by ribonuclease III. In this study, it is shown that the steady state level of the pnp mRNA increased 11‐fold in a ribonuclease III‐deficient strain. The synthesis rate of this messenger is only slightly affected in the mutant strain whereas the half‐life, which is 1.5 min in the wild type, is considerably increased to more than 40 min. Moreover, polynucleotide phosphorylase is 10‐fold over‐expressed in the mutant strain, which shows that unprocessed pnp mRNA is functional. The position of the ribonuclease III‐sensitive site suggests that the sequence involved in the stabilization of the pnp mRNA is located at the 5′ end of the message and that the RNase III processing triggers the decay of the transcripts downstream. A similar function for ribonuclease III in the processing of the messenger for the beta beta' subunits of RNA polymerase is proposed.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.