No abstract

SummaryRT-PCR analysis of the genes in the clavulanic acid cluster revealed three transcriptional polycistronic units that comprised the ceaS2-bls2-pah2-cas2, cyp-fd-orf12-orf13 and oppA2-orf16 genes, whereas oat2, car, oppA1, claR, orf14, gcaS and pbpA were expressed as monocistronic transcripts. Quantitative RT-PCR of Streptomyces clavuligerus ATCC 27064 and the mutant S. clavuligerus ccaR::aph showed that, in the mutant, there was a 1000-to 10 000-fold lower transcript level for the ceaS2 to cas2 polycistronic transcript that encoded CeaS2, the first enzyme of the clavulanic acid pathway that commits arginine to clavulanic acid biosynthesis. Smaller decreases in expression were observed in the ccaR mutant for other genes in the cluster. Two-dimensional electrophoresis and MALDI-TOF analysis confirmed the absence in the mutant strain of proteins CeaS2, Bls2, Pah2 and Car that are required for clavulanic acid biosynthesis, and CefF and IPNS that are required for cephamycin biosynthesis. Gel shift electrophoresis using recombinant r-CcaR protein showed that it bound to the ceaS2 and claR promoter regions in the clavulanic acid cluster, and to the lat, cefF, cefD-cmcI and ccaR promoter regions in the cephamycin C gene cluster. Footprinting experiments indicated that triple heptameric conserved sequences were protected by r-CcaR, and allowed identification of heptameric sequences as CcaR binding sites.

ArgR is the regulator of arginine biosynthesis genes in Streptomyces species. Transcriptomic comparison by microarrays has been made between Streptomyces coelicolor M145 and its mutant S. coelicolor ΔargR under control, unsupplemented conditions, and in the presence of arginine. Expression of 459 genes was different in transcriptomic assays, but only 27 genes were affected by arginine supplementation. Arginine and pyrimidine biosynthesis genes were derepressed by the lack of ArgR, while no strong effect on expression resulted on arginine supplementation. Several nitrogen metabolism genes expression as glnK, glnA and glnII, were downregulated in S. coelicolor ΔargR. In addition, downregulation of genes for the yellow type I polyketide CPK antibiotic and for the antibiotic regulatory genes afsS and scbR was observed. The transcriptomic data were validated by either reverse transcription-PCR, expression of the gene-promoter coupled to the luciferase gene, proteomic or by electrophoresis mobility shift assay (EMSA) using pure Strep-tagged ArgR. Two ARG-boxes in the arginine operon genes suggest that these genes are more tightly controlled. Other genes, including genes encoding regulatory proteins, possess a DNA sequence formed by a single ARG-box which responds to ArgR, as validated by EMSA.