A novel determinant (comA) essential for natural transformation competence in Neisseria gonorrhoeae and the effect of a comA defect on pilin variation.

A novel genetic determinant (comA) has been identified and found to be required for the transformation of piliated Neisseria gonorrhoeae. Mutants in comA of strain MS11 grow normally and are DNA-uptake proficient but blocked in the translocation of DNA into the cytoplasm. Here we show by site-specific mutagenesis and genetic complementation that only one of two open reading frames identified in comA is essential for competence: it encodes a protein (ComA) with a predicted size of 74 kDa. The comA gene maps upstream of the iga locus and is transcribed in the opposite orientation, probably under the control of a putative sigma 54-type promoter. While DNA probes specific for the N. gonorrhoeae iga locus reveal only a little cross-reactivity with commensal Neisseria species, the neighbouring comA gene appears to be present in most of them. ComA fusion proteins were obtained by in vitro translation. The synthesized gene products migrated atypically in SDS gels indicating its strong hydrophobicity. Several transmembrane alpha-helices were predicted from the amino acid sequence of ComA which, in the context of an observed sequence similarity with other inner membrane proteins, suggests a location for the protein in the inner membrane. Using piliated and non-piliated comA mutants the consequences of transformation deficiency on pilin phase variation were assessed. We show that the comA defect affects some but not all types of DNA rearrangements associated with pilE variation. The results are in agreement with previous observations supporting the notion that multiple recombination pathways contribute to the variability of pilE.