Bagyan I, Casillas-Martinez L, Setlow P
Department of Biochemistry, University of Connecticut Health Center, Farmington 06032, USA.
J Bacteriol. 1998 Apr;180(8):2057-62. doi: 10.1128/JB.180.8.2057-2062.1998.
Previous work has shown that the katX gene encodes the major catalase in dormant spores of Bacillus subtilis but that this enzyme has no role in dormant spore resistance to hydrogen peroxide. Expression of a katX-lacZ fusion began at approximately h 2 of sporulation, and >75% of the katX-driven beta-galactosidase was packaged into the mature spore. A mutation in the gene coding for the sporulation-specific RNA polymerase sigma factor sigmaF abolished katX-lacZ expression, while mutations in genes encoding sigmaE, sigmaG, and sigmaK did not. Induction of sigmaF synthesis in vegetative cells also resulted in katX-lacZ expression, while induction of sigmaG expression did not; the katX-lacZ fusion was also not induced by hydrogen peroxide. Upstream of the in vivo katX transcription start site there are sequences with good homology to those upstream of known sigmaF-dependent start sites. These data indicate that katX is an additional member of the forespore-specific sigmaF regulon. A mutant in the katA gene, encoding the major catalase in growing cells, was sensitive to hydrogen peroxide during sporulation, while a katX mutant was not. However, outgrowth of katX spores, but not katA spores, was sensitive to hydrogen peroxide. Consequently, a major function for KatX is to protect germinating spores from hydrogen peroxide.
先前的研究表明，katX基因编码枯草芽孢杆菌休眠孢子中的主要过氧化氢酶，但该酶在休眠孢子对过氧化氢的抗性中不起作用。katX-lacZ融合基因的表达在芽孢形成约2小时时开始，且超过75%由katX驱动的β-半乳糖苷酶被包装到成熟孢子中。编码芽孢形成特异性RNA聚合酶σ因子σF的基因突变消除了katX-lacZ的表达，而编码σE、σG和σK的基因突变则没有。在营养细胞中诱导σF合成也会导致katX-lacZ表达，而诱导σG表达则不会；katX-lacZ融合基因也不会被过氧化氢诱导。在体内katX转录起始位点上游，存在与已知的σF依赖性起始位点上游序列具有高度同源性的序列。这些数据表明，katX是前芽孢特异性σF调控子的另一个成员。编码生长细胞中主要过氧化氢酶的katA基因突变体在芽孢形成过程中对过氧化氢敏感，而katX突变体则不敏感。然而，katX孢子的萌发，而不是katA孢子的萌发，对过氧化氢敏感。因此，KatX的主要功能是保护萌发的孢子免受过氧化氢的伤害。
