Identification and characterization of hydrogen peroxide-sensitive mutants of Escherichia coli: genes that require OxyR for expression.

Escherichia coli produces an inducible set of proteins that protect the cell from exogenous peroxide stress. A subset of these genes is induced by hydrogen peroxide and is controlled at the transcriptional level by the OxyR protein. To identify additional genes involved in protection from hydrogen peroxide, a library of random transcriptional fusions of lambda(plac)Mu53 was screened for hydrogen peroxide sensitivity and 27 such mutants were identified. These fusions were transduced into nonlysogenic strains to ensure that the phenotypes observed were the result of a single mutation. The mutants were grouped into three classes based on the expression of the lacZ fusion during growth in oxyR+ and deltaoxyR backgrounds. The expression of the lacZ fusion in 8 mutants was independent of OxyR, 10 mutants required OxyR for expression, and 6 mutants showed reduced levels of expression in the presence of OxyR. OxyR dependence varied from 2- to 50-fold in these mutants. The OxyR-dependent phenotype was complemented by a plasmid-borne copy of oxyR gene in all mutants. Three mutants exhibited dual regulation by OxyR and RpoS. We sequenced the fusion junctions of several of these mutants and identified the genetic loci responsible for the hydrogen peroxide-sensitive (hps) phenotype. In this study, we report the identification of several genes that require OxyR for expression, including hemF (encoding coproporphyrinogen III oxidase), rcsC (encoding a sensor-regulator protein of capsular polysaccharide synthesis genes), and an open reading frame, f497, that is similar to arylsulfatase-encoding genes.

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