The A-factor regulatory cascade leading to streptomycin biosynthesis in Streptomyces griseus: identification of a target gene of the A-factor receptor

In Streptomyces griseus, A-factor (2-isocapryloyl-3R-hydroxymethyl-gamma-bu tyrolactone) at an extremely low concentration triggers streptomycin biosyn thesis and cell differentiation by binding a repressor-type receptor protei n (ArpA) and dissociating it from DNA, An A-factor-responsive transcription al activator (AdpA) able to bind the promoter of strR, a pathway-specific r egulatory gene responsible for transcription of other streptomycin biosynth etic genes, was purified to homogeneity and adpA was cloned by PCR on the b asis of amino acid sequences of purified AdpA. adpA encoding a 405-amino-ac id protein containing a helix-turn-helix DNA-binding motif at the central r egion showed sequence similarity to transcriptional regulators in the AraC/ XyIS family. The -35 and -10 regions of the adpA promoter were found to be a target of ArpA; ArpA bound the promoter region in the absence of A-factor and exogenous addition of A-factor to the DNA-ArpA complex immediately rel eased ArpA from the DNA, Consistent with this, S1 nuclease mapping showed t hat adpA was transcribed only in the presence of A-factor and strR was tran scribed only in the presence of intact adpA, Furthermore, adpA disruptants produced no streptomycin and overexpression of adpA caused the wild-type S. griseus strain to produce streptomycin at an earlier growth stage in a lar ger amount, On the basis of these findings, we propose here a model to demo nstrate how A-factor triggers streptomycin biosynthesis at a late exponenti al growth stage.