GntR family regulator SCO6256 is involved in antibiotic production and conditionally regulates the transcription of myo-inositol catabolic genes in Streptomyces coelicolor A3(2)

SCO6256 belongs to the GntR family and shows 74% identity with SCO6974, which is the repressor of myo-inositol catabolism in Streptomyces coelicolor A3(2). Disruption of SCO6256 significantly enhanced the transcription of myo-inositol catabolic genes in R2YE medium. The purified recombinant SCO6256 directly bound to the upstream regions of SCO2727, SCO6978 and SCO6985, as well as its encoding gene. Footprinting assays demonstrated that SCO6256 bound to the same sites in the myo-inositol catabolic gene cluster as SCO6974. The expression of SCO6256 was repressed by SCO6974 in minimal medium with myo-inositol as the carbon source, but not in R2YE medium. Glutathione-S-transferase pull-down assays demonstrated that SCO6974 and SCO6256 interacted with each other; and both of the proteins controlled the transcription of myo-inositol catabolic genes in R2YE medium. These results indicated SCO6256 regulates the transcription of myo-inositol catabolic genes in coordination with SCO6974 in R2YE medium. In addition, SCO6256 negatively regulated the production of actinorhodin and calcium-dependent antibiotic via control of the transcription of actII-ORF4 and cdaR. SCO6256 bound to the upstream region of cdaR and the binding sequence was proved to be TTTCGGCACGCAGACAT, which was further confirmed through base substitution. Four putative targets (SCO2652, SCO4034, SCO4237 and SCO6377) of SCO6256 were found by screening the genome sequence of Strep. coelicolor A3(2) based on the conserved binding motif, and confirmed by transcriptional analysis and electrophoretic mobility shift assays. These results revealed that SCO6256 is involved in the regulation of myo-inositol catabolic gene transcription and antibiotic production in Strep. coelicolor A3(2).