Characterization of the recD gene of Neisseria gonorrhoeae MS11 and the Effect of recD Inactivation on Pilin Variation and DNA Transformation
Hill, Stuart A.
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Pilin antigenic variation in Neisseria gonorrhoeae may result following intrachromosomal recombination between homologous pi/ genes. Despite extensive study, recA is the only previously characterized gene known to be involved in this process. In this study, the gonococcal recD gene, encoding one subunit of the putative RecBCD holoenzyme, was characterized and its role in pilin variation assessed. The complete recD gene of N. gonorrhoeae M S l l was cloned and its nucleotide sequence determined. The gonococcal recD gene complemented a defined Escherichia coli recD mutant, based on plaque formation of bacteriophage 1 and the restoration of ATP-dependent nuclease activity. Inactivation of the gonococcal recD 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 nonparental pilin phenotypes were spawned was 12-fold greater in M S l l recD mutants compared with the parental MS11 re& strain. Similar results were obtained using recD mutants that were not competent for DNA transformation. Complementation of the M S l l recD mutant with a wild-type recD gene copy restored the frequency of pilin phenotypic variation to approximately wild-type levels. The nucleotide changes at pi/€ in the recD mutants were confined to the variable regions of the gene and were similar to changes previously attributed to gene conversion.