Hilbert David W, Piggot Patrick J
Department of Microbiology and Immunology, Temple University School of Medicine, Philadelphia, Pennsylvania 19140, USA.
J Bacteriol. 2003 Mar;185(5):1590-8. doi: 10.1128/JB.185.5.1590-1598.2003.
During sporulation, Bacillus subtilis undergoes an asymmetric division that results in two cells with different fates, the larger mother cell and the smaller forespore. The protein phosphatase SpoIIE, which is required for activation of the forespore-specific transcription factor sigma(F), is also required for optimal efficiency and timing of asymmetric division. We performed a genetic screen for spoIIE mutants that were impaired in sporulation but not sigma(F) activity and isolated a strain with the mutation spoIIEV697A. The mutant exhibited a 10- to 40-fold reduction in sporulation and a sixfold reduction in asymmetric division compared to the parent. Transcription of the sigma(F)-dependent spoIIQ promoter was increased more than 10-fold and was no longer confined to the forespore. The excessive sigma(F) activity persisted even when asymmetric division was prevented. Disruption of spoIIGB did not restore asymmetric division to the spoIIEV697A mutant, indicating that the deficiency is not a consequence of predivisional activation of the mother cell-specific transcription factor sigma(E). Deletion of the gene encoding sigma(F) (spoIIAC) restored asymmetric division; however, a mutation that dramatically reduced the number of promoters responsive to sigma(F), spoIIAC561 (spoIIACV233 M), failed to do so. This result suggests that the block is due to expression of one of the small subset of sigma(F)-dependent genes expressed in this background or to unregulated interaction of sigmaF with some other factor. Our results indicate that regulation of SpoIIE plays a critical role in coupling asymmetric division to sigma(F) activation in order to ensure proper spatial and temporal expression of forespore-specific genes.
在芽孢形成过程中,枯草芽孢杆菌会经历不对称分裂,产生两个命运不同的细胞,即较大的母细胞和较小的前芽孢。蛋白磷酸酶SpoIIE是前芽孢特异性转录因子sigma(F)激活所必需的,也是不对称分裂达到最佳效率和适时进行所必需的。我们针对在芽孢形成方面受损但sigma(F)活性未受影响的spoIIE突变体进行了遗传筛选,分离出了一个带有spoIIEV697A突变的菌株。与亲本相比,该突变体的芽孢形成减少了10至40倍,不对称分裂减少了6倍。依赖sigma(F)的spoIIQ启动子的转录增加了10倍以上,并且不再局限于前芽孢。即使阻止了不对称分裂,过量的sigma(F)活性仍然存在。破坏spoIIGB并没有使spoIIEV697A突变体恢复不对称分裂,这表明缺陷并非母细胞特异性转录因子sigma(E)的分裂前激活所致。缺失编码sigma(F)的基因(spoIIAC)可恢复不对称分裂;然而,一个显著减少对sigma(F)响应的启动子数量的突变spoIIAC561(spoIIACV233M)却未能做到这一点。这一结果表明,阻断是由于在此背景下表达的一小部分依赖sigma(F)的基因之一的表达,或者是由于sigmaF与其他一些因子的不受调控的相互作用。我们的结果表明,SpoIIE的调控在将不对称分裂与sigma(F)激活相耦合方面起着关键作用,以确保前芽孢特异性基因在空间和时间上的正确表达。