Mohanty B K, Kushner S R
Department of Genetics, University of Georgia, Athens, GA 30605, USA.
Mol Microbiol. 2000 May;36(4):982-94. doi: 10.1046/j.1365-2958.2000.01921.x.
Poly(A) tails in Escherichia coli are hypothesized to provide unstructured single-stranded substrates that facilitate the degradation of mRNAs by ribonucleases. Here, we have investigated the role that such nucleases play in modulating polyadenylation in vivo by measuring total poly(A) levels, polyadenylation of specific transcripts, growth rates and cell viabilities in strains containing various amounts of poly(A) polymerase I (PAP I), polynucleotide phosphorylase (PNPase), RNase II and RNase E. The results demonstrate that both PNPase and RNase II are directly involved in regulating total in vivo poly(A) levels. RNase II is primarily responsible for degrading poly(A) tails associated with 23S rRNA, whereas PNPase is more effective in modulating the polyadenylation of the lpp and 16S rRNA transcripts. In contrast, RNase E appears to affect poly(A) levels indirectly through the generation of new 3' termini that serve as substrates for PAP I. In addition, whereas excess PNPase suppresses polyadenylation by more than 70%, the toxicity associated with increased poly(A) levels is not reduced. Conversely, toxicity is significantly reduced in the presence of excess RNase II. Overproduction of RNase E leads to increased polyadenylation and no reduction in toxicity.
据推测，大肠杆菌中的聚腺苷酸（Poly(A)）尾可提供无结构的单链底物，便于核糖核酸酶降解信使核糖核酸（mRNA）。在此，我们通过测量含有不同量聚腺苷酸聚合酶I（PAP I）、多核苷酸磷酸化酶（PNPase）、核糖核酸酶II（RNase II）和核糖核酸酶E（RNase E）的菌株中的总聚腺苷酸水平、特定转录本的聚腺苷酸化、生长速率和细胞活力，研究了这些核酸酶在体内调节聚腺苷酸化过程中所起的作用。结果表明，PNPase和RNase II都直接参与调节体内总聚腺苷酸水平。RNase II主要负责降解与23S核糖体RNA相关的聚腺苷酸尾，而PNPase在调节脂蛋白（lpp）和16S核糖体RNA转录本的聚腺苷酸化方面更有效。相比之下，RNase E似乎通过产生作为PAP I底物的新3'末端间接影响聚腺苷酸水平。此外，虽然过量的PNPase可抑制聚腺苷酸化超过70%，但与聚腺苷酸水平升高相关的毒性并未降低。相反，在存在过量RNase II的情况下，毒性显著降低。RNase E的过量表达导致聚腺苷酸化增加且毒性没有降低。
