Summary: Pilin antigenic variation in gonorrhoeae may result following intrachromosomal recombination between homologous genes. Despite extensive study, is the only previously characterized gene known to be involved in this process. In this study, the gonococcal gene, encoding one subunit of the putative REcBCD holoenzyme, was characterized and its role in pilin variation assessed. The complete gene of MS11 was cloned and its nucleotide sequence determined. The gonococcal gene complemented a defined mutant, based on plaque formation of bacteriophage λ and the restoration of ATP-dependent nuclease activity. Inactivation of the gonococcal gene had no measurable effect on cell viability or survival following UV exposure, but did decrease the frequency of DNA transformation approximately threefold. The frequency at which non-parental pilin phenotypes were spawned was 12-fold greater in MS11 mutants compared with the parental MS11 strain. Similar results were obtained using mutants that were not competent for DNA transformation. Complementation of the MS11 mutant with a wild-type gene copy restored the frequency of pilin phenotypic variation to approximately wild-type levels. The nucleotide changes at in the mutants were confined to the variable regions of the gene and were similar to changes previously attributed to gene conversion.


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