부산대학교 도서관

Hierarchical interactions between alternative sigma factors control sequential gene expression in Gram-positive bacteria, whereas alternative sigma factors in Gram-negative bacteria are generally regarded to direct expression of discrete gene subsets. In Salmonella enterica serovar Typhimurium (S. Typhimurium), σ responds to extracytoplasmic stress, whereas σ responds to heat shock and σ is induced during nutrient limitation. Deficiency of σ, σ or σ increases S. Typhimurium susceptibility to oxidative stress, but an analysis of double and triple mutants suggested that antioxidant actions of σ and σ might be dependent on σ. Transcriptional profiling of mutant Salmonella lacking σ revealed reduced expression of genes dependent on σ and σ in addition to σ. Further investigation demonstrated that σ augments σ levels during stationary phase via enhanced expression of σ and the RNA-binding protein Hfq, leading to increased expression of σ-dependent genes and enhanced resistance to oxidative stress. Maximal expression of the σ-regulated gene katE required σ in Salmonella-infected macrophages as well as stationary-phase cultures. Interactions between alternative sigma factors permit the integration of diverse stress signals to produce coordinated genetic responses.