Cao G J, Sarkar N
Boston Biomedical Research Institute, Massachusetts 02114, USA.
Biochem Biophys Res Commun. 1997 Oct 9;239(1):46-50. doi: 10.1006/bbrc.1997.7421.
Polyadenylation of Escherichia coli specific mRNAs has so far been studied primarily during the exponential phase of growth. As part of an investigation of the polyadenylation of E. coli mRNAs in different physiological contexts, we studied mRNA polyadenylation in stationary phase by preparing a cDNA library from stationary phase RNA using oligodeoxythymidylate primers and analyzing the nucleotide sequence of cDNA clones corresponding to the stationary phase-specific genes, rpoS, bo1A, and dps. The sites of polyadenylation were found to be primarily in the 3'-untranslated region, either at the putative rho-independent transcription termination site (dps) or at several different sites upstream of the putative rho-independent terminator. A few examples of polyadenylation within the coding regions were also found, suggesting that nucleolytic degradation often preceded polyadenylation. In contrast to the poly(A) tracts characteristic of exponentially growing cells, many of the uncoded poly(A) tracts associated with stationary phase mRNA were interspersed with other nucleotide residues. The observation of post-transcriptional polyadenylation of specific stationary phase mRNAs in E. coli, some of which are transcribed by the RNA polymerase associated with sigma, demonstrates that mRNA polyadenylation is not confined to the exponential phase of growth.
迄今为止，对大肠杆菌特异性mRNA的聚腺苷酸化研究主要集中在生长指数期。作为对不同生理环境下大肠杆菌mRNA聚腺苷酸化研究的一部分，我们通过使用寡聚脱氧胸苷酸引物从稳定期RNA制备cDNA文库，并分析与稳定期特异性基因rpoS、bo1A和dps相对应的cDNA克隆的核苷酸序列，来研究稳定期的mRNA聚腺苷酸化。结果发现，聚腺苷酸化位点主要位于3'非翻译区，要么在假定的不依赖ρ因子的转录终止位点（dps）处，要么在假定的不依赖ρ因子的终止子上游的几个不同位点处。在编码区内也发现了一些聚腺苷酸化的例子，这表明核酸酶降解通常先于聚腺苷酸化。与指数生长细胞特有的聚（A）尾不同，许多与稳定期mRNA相关的未编码聚（A）尾都穿插有其他核苷酸残基。在大肠杆菌中观察到特定稳定期mRNA的转录后聚腺苷酸化，其中一些是由与σ因子相关的RNA聚合酶转录的，这表明mRNA聚腺苷酸化并不局限于生长指数期。
