THE PRODUCT OF THE PILQ GENE IS ESSENTIAL FOR THE BIOGENESIS OF TYPE-IV PILI IN NEISSERIA-GONORRHOEAE

The product of the Neisseria gonorrhoeae omc gene possesses regions ho mologous to those found in members of a protein superfamily that are a ssociated with the translocation of proteins and DNA-protein complexes across the outer membrane. Amongst its protein homologues, Omc has hi gher overall homology to PilQ, which is required for type IV pilus exp ression in Pseudomonas aeruginosa, and OrfE, which is required for seq uence-specific DNA uptake by Haemophilus influenzae. The function of O mc, however, is unknown and gonococcal omc mutants have not been descr ibed. We constructed gonococcal mutants expressing truncated forms of the protein, and found that these mutants are severely defective for b oth pilus expression and competence for natural transformation. To be consistent with pre-existing pilus gene nomenclature, we have redesign ated the gene pilQ instead of omc, and its product, PilQ instead of Om c. The MS11 gene was sequenced and found to differ from the DNA sequen ce reported for that of another gonococcal strain; these differences w ere associated with a repeated DNA element, suggesting a genetic basis for structural variation in PilQ. The results also show that PilQ(-) mutants are distinct from previously described gonococcal pilus-assemb ly mutants and P. aeruginosa PilQ(-) mutants by virtue of their expres sion of rare pilus filaments. Taking these data into account, PilQ is proposed to function in the terminal steps of organelle biogenesis by acting as a pilus channel or pore.