Errington J, Feucht A, Lewis P J, Lord M, Magnin T, Najafi S M, Wilkinson J F, Yudkin M D
Sir William Dunn School of Pathology, University of Oxford, U.K.
Philos Trans R Soc Lond B Biol Sci. 1996 Apr 29;351(1339):537-42. doi: 10.1098/rstb.1996.0052.
Sporulation in Bacillus subtilis is a simple developmental system involving the differentiation of two cell types that are formed by an asymmetric cell division. Major changes in the pattern of transcription during sporulation are brought about by the synthesis of new sigma factors (sigma), which are subunits of RNA polymerase that determine promoter specificity. Transcription in the smaller prespore cell type is initiated by a sigma factor called sigma F, the activity of which is subject to tight spatial and temporal control. It is negatively regulated by an anti-sigma factor, SpoIIAB, which is in turn controlled by an anti-anti-sigma factor, SpoIIAA. SpoIIAA and SpoIIAB participate in two contrasting reactions in vitro. In the presence of ATP, the proteins interact transiently and SpoIIAA is inactivated by phosphorylation on a specific serine residue; SpoIIAA then remains free to inhibit sigma F. In the presence of ADP, SpoIIAA binds tightly to SpoIIAB, and sigma F is set free. Release of sigma F activity in vivo might thus be effected by a prespore-specific reduction in the ATP/ADP ratio. Genetic experiments have implicated a fourth protein, called SpoIIE, in this system. It now appears that SpoIIE has two important and independent functions in the establishment of the prespore-specific transcription by sigma F. First it regulates sigma F activity, probably acting as a phosphatase to regenerate the active, non-phosphorylated form of SpoIIAA. Second it controls the formation of the septum that generates the prespore compartment. Combination of these two functions in a single polypeptide may provide a means of coupling gene expression with morphogenesis.
枯草芽孢杆菌的孢子形成是一个简单的发育系统，涉及通过不对称细胞分裂形成的两种细胞类型的分化。孢子形成过程中转录模式的主要变化是由新的σ因子（sigma）的合成引起的，σ因子是RNA聚合酶的亚基，决定启动子特异性。较小的前芽孢细胞类型中的转录由一种称为σF的σ因子启动，其活性受到严格的空间和时间控制。它受到一种抗σ因子SpoIIAB的负调控，而SpoIIAB又由一种抗抗σ因子SpoIIAA控制。SpoIIAA和SpoIIAB在体外参与两种相反的反应。在ATP存在下，这些蛋白质短暂相互作用，SpoIIAA在特定丝氨酸残基上被磷酸化而失活；然后SpoIIAA保持游离状态以抑制σF。在ADP存在下，SpoIIAA与SpoIIAB紧密结合，σF被释放。因此，体内σF活性的释放可能是由前芽孢特异性的ATP/ADP比值降低所导致的。遗传实验表明该系统中还有第四种蛋白质，称为SpoIIE。现在看来，SpoIIE在由σF建立前芽孢特异性转录过程中具有两个重要且独立的功能。首先，它调节σF活性，可能作为一种磷酸酶来再生活性的、未磷酸化形式的SpoIIAA。其次，它控制产生前芽孢隔室的隔膜的形成。在单一多肽中结合这两种功能可能提供一种将基因表达与形态发生偶联的方式。
