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Role Of OxyR As A Peroxide-Sensing Positive Regulator In Streptomyces Coelicolor A3(2)

Ji-Sook Hahn, So-Young Oh, Jung-Hye Roe

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ABSTRACT Genes encoding a homolog of Escherichia coli OxyR ( oxyR ) and an alkyl hydroperoxide reductase system ( ahpC and ahpD ) have been isolated from Streptomyces coelicolor A3(2). The ahpC and ahpD genes constitute an operon transcribed divergently from the oxyR gene . Expression of both ahpCD and oxyR genes was maximal at early exponential phase and decreased rapidly as cells entered mid-exponential phase. Overproduction of OxyR in Streptomyces lividans conferred resistance against cumene hydroperoxide and H 2 O 2 . The oxyR mutant produced fewer ahpCD and oxyR transcripts than the wild type, suggesting that OxyR acts as a positive regulator for their expression. Both oxyR and ahpCD transcripts increased more than fivefold within 10 min of H 2 O 2 treatment and decreased to the normal level in 50 min, with kinetics similar to those of the CatR-mediated induction of the catalase A gene ( catA ) by H 2 O 2 . The oxyR mutant failed to induce oxyR and ahpCD genes in response to H 2 O 2 , indicating that OxyR is the modulator for the H 2 O 2 -dependent induction of these genes. Purified OxyR protein bound specifically to the intergenic region between ahpC and oxyR , suggesting its direct role in regulating these genes. These results demonstrate that in S. coelicolor OxyR mediates H 2 O 2 induction of its own gene and genes for alkyl hydroperoxide reductase system, but not the catalase gene ( catA ), unlike in Escherichia coli and Salmonella enterica serovar Typhimurium.