Boylan S A, Redfield A R, Price C W
Department of Food Science and Technology, University of California, Davis 95616.
J Bacteriol. 1993 Jul;175(13):3957-63. doi: 10.1128/jb.175.13.3957-3963.1993.
Transcription factor sigma B of Bacillus subtilis is active during the stationary growth phase, but its physiological role remains unknown. Understanding the function and regulation of genes controlled by sigma B (csb genes) should provide important clues to sigma B function in stationary-phase cells. To this end, we used a genetic approach to identify six new csb genes. This strategy relies on two elements: (i) random transcriptional fusions between the Escherichia coli lacZ gene and genes on the B. subtilis chromosome, generated in vivo with transposon Tn917lacZ, and (ii) a plate transformation technique to introduce a null sigB mutation into the fusion-bearing recipients directly on indicator plates. This strategy allowed the comparison of fusion expression in strains that were isogenic save for the presence or absence of a functional sigma B protein. Beginning with 1,400 active fusions, we identified 11 that were wholly or partly controlled by sigma B. These fusions mapped to six different loci that exhibit substantial contrasts in their patterns of expression in the logarithmic and stationary growth phases, suggesting that they participate in diverse cellular functions. However, for all six loci, the sigma B-dependent component of their expression was manifest largely in the stationary phase. The high frequency of six independent csb loci detected in a random collection of 1,400 fusions screened, the fact that four of the six new loci were defined by a single fusion, and the absence of the previously identified ctc and csbA genes in the present collection strongly suggest that sigma B controls a large stationary-phase regulon.
枯草芽孢杆菌的转录因子σB在稳定生长期具有活性，但其生理作用尚不清楚。了解由σB控制的基因（csb基因）的功能和调控，应该能为σB在稳定期细胞中的功能提供重要线索。为此，我们采用遗传学方法鉴定了6个新的csb基因。该策略依赖于两个要素：（i）利用转座子Tn917lacZ在体内产生大肠杆菌lacZ基因与枯草芽孢杆菌染色体上基因之间的随机转录融合，以及（ii）一种平板转化技术，直接在指示平板上向携带融合基因的受体中引入σB基因的无效突变。该策略允许比较除了有无功能性σB蛋白外其他基因相同的菌株中融合基因的表达情况。从1400个活性融合基因开始，我们鉴定出11个完全或部分受σB控制的融合基因。这些融合基因定位于6个不同的位点，它们在对数生长期和稳定生长期的表达模式存在显著差异，表明它们参与了多种细胞功能。然而对于所有6个位点，其表达中依赖σB的成分主要在稳定期表现出来。在筛选的1400个融合基因的随机集合中检测到6个独立的csb位点的高频率，6个新位点中有4个由单个融合基因定义，以及在当前集合中未发现先前鉴定的ctc和csbA基因，这些强烈表明σB控制着一个大型的稳定期调控子。
