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Sequencing of the DNA region on the left fringe of the pimaricin gene cluster revealed the presence of a 3.6-kb gene, pimR, whose deduced product (1,198 amino acid residues) was found to have amino acid sequence homology with bacterial regulatory proteins. Database comparisons revealed that PimR represents the archetype of a new class of regulators, combining a Streptomyces antibiotic regulatory protein (SARP)-like N-terminal section with a C-terminal half homologous to guanylate cyclases and large ATP-binding regulators of the LuxR family. Gene replacement of pimR from Streptomyces natalensis chromosome results in a complete loss of pimaricin production, suggesting that PimR is a positive regulator of pimaricin biosynthesis. Gene expression analysis by reverse transcriptase PCR (RT-PCR) of the pimaricin gene cluster revealed that S. natalensis ΔPimR shows no expression at all of the …