The Escherichia coli FNR protein is an oxygen-responsive global transcription factor, and OxyR is a key regulator of the peroxide stress response. Here both FNR and OxyR are shown to regulate expression of the E. coli yhjA gene. The yhjA gene encodes a predicted cytochrome c peroxidase, a bacterial haem-containing protein involved in the peroxide stress response through its ability to convert hydrogen peroxide to water. It is shown that the yhjA gene of E. coli possesses a class II FNR site and an OxyR site upstream of the yhjA transcript start. Expression of yhjA was found to be dependent on this unusual combination of FNR and OxyR under conditions of oxygen starvation. Phenotypic analysis of the yhjA mutant revealed increased sensitivity to exogenous hydrogen peroxide and organic peroxides during growth under anaerobic conditions, consistent with the observed regulation and predicted function of the yhjA gene product.
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