Pleiotropic Functions of a Streptomyces pristinaespiralisAutoregulator Receptor in Development, Antibiotic Biosynthesis, and Expression of a Superoxide Dismutase*

In Streptomyces, a family of related butyrolactones and their corresponding receptor proteins serve as quorum-sensing systems that can activate morphological development and antibiotic biosynthesis. Streptomyces pristinaespiraliscontains a gene cluster encoding enzymes and regulatory proteins for the biosynthesis of pristinamycin, a clinically important streptogramin antibiotic complex. One of these proteins, PapR1, belongs to a well known family of Streptomycesantibiotic regulatory proteins. Gel shift assays using crude cytoplasmic extracts detected SpbR, a developmentally regulated protein that bound to the papR1promoter. SpbR was purified, and its gene was cloned using reverse genetics. spbRencoded a 25-kDa protein similar to Streptomycesautoregulatory proteins of the butyrolactone receptor family, including scbRfrom Streptomyces coelicolor. In Escherichia coli, purified SpbR and ScbR produced bound sequences immediately upstream of papR1, spbR, and scbR. SpbR DNA-binding activity was inhibited by an extracellular metabolite with chromatographic properties similar to those of the well known γ-butyrolactone signaling compounds. DNase I protection assays mapped the SpbR-binding site in the papR1promoter to a sequence homologous to other known butyrolactone autoregulatory elements. A nucleotide data base search showed that these binding motifs were primarily located upstream of genes encoding Streptomycesantibiotic regulatory proteins and butyrolactone receptors in various Streptomycesspecies. Disruption of the spbRgene in S. pristinaespiralisresulted in severe defects in growth, morphological differentiation, pristinamycin biosynthesis, and expression of a secreted superoxide dismutase.