Molecular principles of antigenic variation in Neisseria gonorrhoeae.

The genome of Neisseria gonorrhoeae harbours many gene loci for the production of variant pili. Strain MS11 has two expression genes (pilE) with promoter and complete coding sequences. The remaining genes are silent (pilS) lacking the promoter and the conservative amino terminals coding sequences of pilin. The pilus genes consist of six variable minicassettes (mc's), that are flancked by strictly conserved sequences. Upon phase (P+ to P+) and antigenic (P+ to P-, or vice versa) transitions minicassettes from silent loci are transferred from silent pilus gene copies to the expression gene by gene conversion. P- variants resulting from such rearrangements still produce pilin mRNA as well as pilin, but only a few are found on the surface of those gonococci.