SIGMA-E IS REQUIRED FOR THE PRODUCTION OF THE ANTIBIOTIC ACTINOMYCIN IN STREPTOMYCES-ANTIBIOTICUS

The phsA gene encodes phenoxazinone synthase (PHS), which catalyses th e penultimate step in the pathway for actinomycin biosynthesis in Stre ptomyces antibioticus. The phsA promoter strikingly resembles a putati ve Streptomyces sigma(E) cognate promoter, and purified E sigma(E) hol oenzyme transcribed the phsA promoter in vitro. However, the phsA prom oter was still active in an S. antibioticus sigE null mutant and the l evel of PHS activity was unaffected. Despite this, disruption of sigE blocked actinomycin production completely. The loss of actinomycin pro duction correlated with a 10-fold decrease in the activity of actinomy cin synthetase I, the enzyme which catalyses the activation of the pre cursor of the actinomycin chromophore.