IDENTIFICATION AND CHARACTERIZATION OF PILG, A HIGHLY CONSERVED PILUS-ASSEMBLY GENE IN PATHOGENIC NEISSERIA

Expression of type IV pill appears to be a requisite determinant of in fectivity for the strict human pathogens Neisseria gonorrhoeae and Nei sseria meningitidis. The assembly of these colonization factors is a c omplex process. This report describes a new pilus-assembly gene, pilG, that immediately precedes the gonococcal (Gc) pilD gene encoding the pre-pilin leader peptidase. The nucleotide sequence of this region rev ealed a single complete open reading frame whose derived polypeptide d isplayed significant identities to the pilus-assembly protein PilC of Pseudomonas aeruginosa and other polytopic integral cytoplasmic membra ne constituents involved in protein export and competence. A unique po lypeptide of M(r) 38 kDa corresponding to the gene product was identif ied. A highly related gene and flanking sequences were cloned from a g roup B polysaccharide-producing strain of N. meningitidis (Me). The re sults indicate that the pilG genes and genetic organization at these l oci in Gc and Me are extremely conserved. Hybridization studies strong ly suggest that pilG-related genes exist in commensal Neisseria specie s and other species known to express type IV pill. Defined genetic les ions were created by using insertional and transposon mutagenesis and moved into the Gc and Me chromosomes by allelic replacement. Chromosom al pilG insertion mutants were devoid of pill and displayed dramatical ly reduced competence for transformation. These findings could not be ascribed to pilin-gene alterations or to polarity exerted on pilD expr ession. The results indicated that PilG exerts its own independent rol e in neisserial pilus biogenesis.