H2O2-sensitive fur-like repressor CatR regulating the major catalase gene in Streptomyces coelicolor

Streptomyces coelicolor produces three distinct catalases to cope with oxid ative and osmotic stresses and allow proper growth and differentiation. The major vegetative catalase A (CatA) is induced by H2O2 and is required for efficient aerobic growth. In order to investigate the H2O2-dependent regula tory mechanism, an H2O2-resistant mutant (HR40) overproducing CatA was isol ated from S. coelicolor A3(2). Based on the genetic map location of the mut ated locus in HR40, the wild type catR gene was isolated from the ordered c osmid library of S. coelicolor by screening for its ability to suppress the HR40 phenotype. catR encodes a protein of 138 amino acids (15319 Da), with sequence homology to ferric uptake regulator (Fur)-like proteins. Disrupti on of catR caused CatA overproduction as observed in the HR40 mutant, confi rming the role of CatR as a negative regulator of catA expression. The leve ls of catA and catR transcripts were higher in HR40 than in the wild type, implying that CatR represses transcription of these genes. Transcripts from the catA and catR genes were induced within 10 min of H2O2 treatment, sugg esting that the repressor activity of CatR may be directly modulated by H2O 2. A putative CatR-binding site containing an inverted repeat of 23 base pa irs was localized upstream of the catA and catR gene, on the basis of seque nce comparison and deletion analysis, CatR protein purified in the presence of dithiothreitol bound to this region, whereas oxidized CatR, treated wit h H2O2 or diamide, did not. The redox shift of CatR involved thiol-disulfid e exchange as judged by modification of free thiols with 4-acetamido-4'-mal eimidylstilbene-2,2'-disulfonate. From these results we propose that CatR r egulates its downstream target genes as a repressor whose DNA binding abili ty is directly modulated by redox changes in the cell.