Regulation of secondary metabolism and cellular differentiation by A-factor and signal transduction systems in Streptomyces

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1. A-factor is a microbial hormone controlling streptomycin production and sporulation. An A-factor-dependent promoter, the strR promoter, in the streptomycin biosynthetic gene cluster of S.griseus was identified. Gel retardation assays detected a protein that specifically bound the strR promoter.2. The AfsR protein is essential for the biosynthesis of A-factor, actinorhodin, and undecylprodigiosin in S.coelicolor. The AfsR protein was purified to homogeneity and found to be phosphorylated by a specific kinase. It is conceivable that the extent of phosphorylation of AfsR modulates its regulatory activity which, in turn, regulates expression of some target genes involved in secondary metabolism in this strain.3. In vitro phosphorylation reactions using extracts of S.griseus cells revealed the presence of multiple phosphorylated proteins. Most of these phosphorylations were distinctly inhibited by staurosporine and K-252a which are known to be eucaryotic protein kinase inhibitors. Consistent with this, these kinase inhibitors inhibited antibiotic production and aerial mycelium formation in S.griseus and S.coelicolor.