ABSTRACT
As free-living non-motile saprophytes, Streptomyces need to adapt to a wide range of environmental conditions and this is reflected by an enormous diversity of regulatory proteins encoded by, for example, the genome of the model streptomycete Streptomyces coelicolor. In this organism, we have identified a new osmoregulation gene, osaC, encoding a member of a novel family of regulatory proteins. Members of the family have a predicted domain composition consisting of an N-terminal kinase domain related to anti-sigma factors, sensory Pas and Gaf domains, and a C-terminal phosphatase domain. osaC is linked to the response regulator gene osaB; expression analysis of the latter revealed that it is induced after osmotic stress in a sigma(B)-dependent manner. OsaC is required to return osaB and sigB expression back to constitutive levels after osmotic stress. From analysis of the activities of OsaC(DeltaPho), lacking the C-terminal phosphatase domain, and OsaC(N92A), with a substitution of a critical asparagine residue in the kinase domain, we infer that this N-terminal domain functions as a sigma(B) anti-sigma factor. Indeed, co-purification experiments indicate association of OsaC and sigma(B). These results support a model for post-osmotic stress modulation of sigma(B) activity by OsaC.
Subject(s)
Bacterial Proteins/metabolism , Sigma Factor/metabolism , Streptomyces coelicolor/metabolism , Water-Electrolyte Balance , Amino Acid Sequence , Gene Expression Regulation, Bacterial , Genes, Bacterial , Molecular Sequence Data , Osmotic Pressure , Promoter Regions, Genetic , Protein Interaction Domains and Motifs , RNA, Bacterial/metabolism , Sequence Alignment , Streptomyces coelicolor/geneticsABSTRACT
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 sigmaH. 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 sigmaH, 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 sigmaH, 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 sigmaH, we assume that sigmaJ may play a role in the later stages of development of S. coelicolor A3(2).
