The opcA and psi opcB regions in Neisseria: genes, pseudogenes, deletions,insertion elements and DNA islands

Previous data have indicated that the ope gene encoding an immunogenic inva sin is specific to Neisseria meningitidis (Nm) and is lacking in Neisseria gonorrhoeae (Ng). The data presented here show that Nm and Ng both contain two paralogous opc-like genes, opcA, corresponding to the former ope gene, and Psi opcB, a pseudogene. The predicted OpcA and OpcB proteins possess tr ansmembrane regions with conserved non-polar faces but differ extensively i n four of the five surface-exposed loops. Gonococcal OpcA was expressed wea kly under in vitro conditions, and it is unknown whether these bacteria can express this protein at high levels. Analysis of the sequences flanking op cA and Psi opcB revealed a framework of conserved housekeeping genes inters persed with DNA islands. These regions also contained several pseudogenes, deletions and IS elements, attesting to considerable genome plasticity. Bot h opcA and Psi opcB are located on DNA islands that have probably been impo rted from unrelated bacteria. A third island encodes the dcmD/dcrD R/M gene s in Ng Versus a small open reading frame in most strains of Nm. Rare strai ns of Nm were identified in which the R/M island has been imported. DNA isl ands in Nm and Ng seem to have been acquired by recombination via conserved flanking housekeeping genes rather than by insertion of mobile genetic ele ments.