Null Mutation of HvrA Compensates for Loss of an Essential relA/spoT -Like Gene in Rhodobacter capsulatus

We report that a single relA/spoT-like gene exists on the Rhodobacter capsulatus chromosome, and its mutational loss is lethal. This gene could be mutated only under a mutational background of a null mutation in the nucleoid protein HvrA. This result suggests that there may be a direct link between HvrA-regulated promoters and the ppGpp-related stringent response.