Cascade of sigma factors in streptomycetes: identification of a new extracytoplasmic function sigma factor σJ that is under the control of the stress-response sigma factor σH in Streptomyces coelicolor A3(2)

By using the previously established Escherichia coli two-plasmid system, we identified a promoter recognized by the Streptomyces coelicolor A3(2) stress-response sigma factor σH. The promoter directed expression of the sigJ gene encoding an extracytoplasmic function (ECF) sigma factor. S1-nuclease mapping using RNA prepared from E. coli containing the two-plasmid system, and S. coelicolor A3(2) from various developmental stages identified an identical transcription start point in both strains, corresponding to the sigJp promoter. The sigJp promoter was induced during sporulation of aerial hyphae. The level of the transcript from sigJp was dramatically reduced in a S. coelicolor A3(2) sigH mutant and unaffected in a sigF mutant. The S. coelicolor A3(2) core RNA polymerase, after complementation with σH, was able to recognize the sigJp promoter in vitro. A sigJ mutation had no obvious effect on growth, stress response, differentiation, and production of antibiotics. The results suggested that the S. coelicolor A3(2) sigJ gene is under the control of stress-response σH, thus indicating a cascade of sigma factors in Streptomyces stress response and development. Considering the expression of sigJ and its direct dependence upon developmentally-regulated σH, we assume that σJ may play a role in the later stages of development of S. coelicolor A3(2).