Lewis P J, Magnin T, Errington J
Sir William Dunn School of Pathology, University of Oxford, UK.
Genes Cells. 1996 Oct;1(10):881-94. doi: 10.1046/j.1365-2443.1996.750275.x.
Differential gene expression during sporulation in the prespore and mother cell of Bacillus subtilis is dependent on the correct timing and localization of the activity of specific transcription (sigma) factors. The first sigma factor activated is sigmaF, which directs gene expression specifically in the prespore compartment. Release of sigmaF activity is tightly controlled through a series of complex interactions involving an anti-sigma factor, SpoIIAB, an anti-anti-sigma factor SpoIIAA and a phosphoprotein phosphatase SpoIIE. In vitro studies have shown that SpoIIAB binds to sigmaF, preventing transcription of the sigmaF regulon, and that it can also phosphorylate SpoIIAA, thereby inactivating it. However, non-phosphorylated SpoIIAA can displace sigmaF from SpoIIAB. The SpoIIE phosphatase provides a means of reactivating SpoIIAA-P.
We have directly determined the cellular distributions of sigmaF, SpoIIAB, SpoIIAA-P and SpoIIAA during sporulation, using recently developed immunofluorescence methods. While sigmaF activity is restricted to the prespore, the protein is present in both compartments. As development proceeds the sigmaF signal disappears. The anti-sigma factor SpoIIAB is also distributed throughout both cells and rapidly disappears from both cellular compartments soon after sigmaF becomes active. Disappearance of SpoIIAB seems to be closely associated with the activation of the second prespore-specific sigma factor sigmaF. The distribution of phosphorylated SpoIIAA closely mimics that of SpoIIAB, being non-compartmentalized and disappearing soon after sigmaF activation occurs. Significantly, the active, non-phosphorylated form of the anti-anti-sigma factor, SpoIIAA, accumulates in the prespore just before sigmaF becomes active.
These results support the hypothesis that the accumulation of SpoIIAA within the prespore is the single most important requirement for activation of sigmaF.
枯草芽孢杆菌前芽孢和母细胞在芽孢形成过程中的差异基因表达取决于特定转录（σ）因子活性的正确时间和定位。第一个被激活的σ因子是σF，它特异性地指导前芽孢区室中的基因表达。σF活性的释放通过一系列复杂的相互作用受到严格控制，这些相互作用涉及一个抗σ因子SpoIIAB、一个抗抗σ因子SpoIIAA和一个磷蛋白磷酸酶SpoIIE。体外研究表明，SpoIIAB与σF结合，阻止σF调控子的转录，并且它还可以使SpoIIAA磷酸化，从而使其失活。然而，未磷酸化的SpoIIAA可以将σF从SpoIIAB中置换出来。SpoIIE磷酸酶提供了一种重新激活SpoIIAA-P的方式。
我们使用最近开发的免疫荧光方法直接确定了芽孢形成过程中σF、SpoIIAB、SpoIIAA-P和SpoIIAA在细胞内的分布。虽然σF活性仅限于前芽孢，但该蛋白存在于两个区室中。随着发育的进行，σF信号消失。抗σ因子SpoIIAB也分布在两个细胞中，并且在σF激活后不久很快从两个细胞区室中消失。SpoIIAB的消失似乎与第二个前芽孢特异性σ因子σG的激活密切相关。磷酸化的SpoIIAA的分布与SpoIIAB非常相似，没有区室化，并且在σF激活后不久就消失了。值得注意的是，抗抗σ因子SpoIIAA的活性、未磷酸化形式在σF激活前就在前芽孢中积累。
这些结果支持了这样一种假设，即SpoIIAA在前芽孢内的积累是激活σF的唯一最重要的条件。
