Carabetta Valerie J, Mohanty Bijoy K, Kushner Sidney R, Silhavy Thomas J
Department of Molecular Biology, Princeton University, Princeton, NJ 08544, USA.
J Bacteriol. 2009 Nov;191(22):6812-21. doi: 10.1128/JB.00870-09. Epub 2009 Sep 18.
In Escherichia coli, the adaptor protein SprE (RssB) controls the stability of the alternate sigma factor RpoS (sigma(38) and sigma(S)). When nutrients are abundant, SprE binds RpoS and delivers it to ClpXP for degradation, but when carbon sources are depleted, this process is inhibited. It also has been noted that overproduction of SprE is toxic. Here we show that null mutations in pcnB, encoding poly(A) polymerase I (PAP I), and in hfq, encoding the RNA chaperone Hfq, suppress this toxicity. Since PAP I, in conjunction with Hfq, is responsible for targeting RNAs, including mRNAs, for degradation by adding poly(A) tails onto their 3' ends, these data indicate that SprE helps modulate the polyadenylation pathway in E. coli. Indeed, in exponentially growing cells, sprE deletion mutants exhibit significantly reduced levels of polyadenylation and increased stability of specific mRNAs, similar to what is observed in a PAP I-deficient strain. In stationary phase, we show that SprE changes the intracellular localization of PAP I. Taken together, we propose that SprE plays a multifunctional role in controlling the transcriptome, regulating what is made via its effects on RpoS, and modulating what is degraded via its effects on polyadenylation and turnover of specific mRNAs.
在大肠杆菌中，衔接蛋白SprE（RssB）控制着替代σ因子RpoS（σ38和σS）的稳定性。当营养丰富时，SprE结合RpoS并将其递送至ClpXP进行降解，但当碳源耗尽时，这一过程受到抑制。也有人指出，SprE的过量表达具有毒性。在此我们表明，编码聚腺苷酸聚合酶I（PAP I）的pcnB和编码RNA伴侣蛋白Hfq的hfq中的无效突变可抑制这种毒性。由于PAP I与Hfq共同负责通过在包括mRNA在内的RNA的3'末端添加聚腺苷酸尾来靶向其进行降解，这些数据表明SprE有助于调节大肠杆菌中的聚腺苷酸化途径。实际上，在指数生长的细胞中，sprE缺失突变体表现出聚腺苷酸化水平显著降低以及特定mRNA稳定性增加，这与在PAP I缺陷菌株中观察到的情况相似。在稳定期，我们表明SprE改变了PAP I的细胞内定位。综上所述，我们提出SprE在控制转录组方面发挥着多功能作用，通过其对RpoS的影响来调节合成的物质，并通过其对特定mRNA的聚腺苷酸化和周转的影响来调节被降解的物质。
