A homologue of the recombination-dependent growth gene, rdgC, is involved in gonococcal pilin antigenic variation

Neisseria gonorrhoeae pilin undergoes high-frequency changer; in primary am ino acid sequence that aid in the avoidance of the host immune response and alter pilus expression. The pilin amino acid changes reflect nucleotide ch anges in the expressed gene, pilE, which result from nonreciprocal recombin ation reactions with numerous silent loci, pilS A Series of mini-transposon insertions affecting pilin antigenic variation were localized to three gen es in one region of the cc chromosome. Mutational analysis with complementa tion showed that a Gc gene with sequence similarity to the Escherichia coli rdgC gene is involved in pilus-dependent colony phase variation and in pil in antigenic variation. Furthermore, Mle show that the Gc rdgC homologue is transcriptionally linked in an operon with a gene encoding a predicted GTP ase. The inability to disrupt expression of this gene suggests it is an ess ential gene (engA, essential neisserial GTPase). While some of the transpos on mutations in rdgC anti insertions in the 5'-untranslated portion of engA showed a growth defect, all transposon insertions investigated conferred a n aberrant cellular morphology. Complementation analysis showed that the gr owth deficiencies are due to the interruption of RdgC expression and not th at of EngA. The requirement of RdgC for efficient pilin variation suggests a role for this protein in specialized DNA recombination reactions.