Yeh Melody, Kelly Keilen, Misra Rajeev
School of Life Sciences, Arizona State University, Tempe, Arizona, USA.
Mol Microbiol. 2025 Jul 9. doi: 10.1111/mmi.70011.
Bacterial cells activate stress-sensing and stress-mitigating pathways by employing a number of transcription regulators, some of which can bind directly to RNA polymerase to activate stress-specific response pathways. However, mutations in the RNA polymerase genes can accumulate under certain selection conditions and activate stress-mitigating pathways in a manner that is partly independent of pathway-specific regulators. In this study, we characterized a novel mutation in the rpoB gene that transforms RNA polymerase into a "stringent" polymerase in the absence of one of the key stringent response (SR) activating factors (p)ppGpp, produced by the relA gene product. The mutant RNA polymerase allele, rpoB58, elevated thermotolerance and permitted growth without the key molecular chaperones (DnaKJ) and proteases (Lon, ClpP) at temperatures nonpermissive to cells expressing the wild type RNA polymerase genes. Remarkably, rpoB58 also reversed the cell division defect of ΔdnaJ at a nonpermissive temperature but could not overcome its lambda phage-resistant phenotype. The rpoB58-mediated rescue of the ΔdnaKJ growth defect was partly reversed in the absence of DksA, a protein that acts synergistically with (p)ppGpp to transform RNA polymerase into a stringent state. The data suggest that pre-activated SR confers thermotolerance and chaperone independence in part by lowering protein synthesis.
细菌细胞通过利用多种转录调节因子来激活应激感应和应激缓解途径，其中一些调节因子可直接与RNA聚合酶结合，以激活应激特异性反应途径。然而，在某些选择条件下，RNA聚合酶基因中的突变可能会积累，并以部分独立于途径特异性调节因子的方式激活应激缓解途径。在本研究中，我们鉴定了rpoB基因中的一种新突变，该突变在缺乏由relA基因产物产生的关键严紧反应（SR）激活因子之一（p）ppGpp的情况下，将RNA聚合酶转变为“严紧”聚合酶。突变的RNA聚合酶等位基因rpoB58提高了耐热性，并允许在对于表达野生型RNA聚合酶基因的细胞而言为非允许温度下，在没有关键分子伴侣（DnaKJ）和蛋白酶（Lon、ClpP）的情况下生长。值得注意的是，rpoB58在非允许温度下也逆转了ΔdnaJ的细胞分裂缺陷，但无法克服其抗λ噬菌体表型。在没有DksA的情况下，rpoB58介导的对ΔdnaKJ生长缺陷的挽救作用部分被逆转，DksA是一种与（p）ppGpp协同作用将RNA聚合酶转变为严紧状态的蛋白质。数据表明，预激活的SR部分通过降低蛋白质合成赋予耐热性和伴侣独立性。
