VARIABLE EXPRESSION OF THE OPC OUTER-MEMBRANE PROTEIN IN NEISSERIA-MENINGITIDIS IS CAUSED BY SIZE VARIATION OF A PROMOTER CONTAINING POLY-CYTIDINE

Opa proteins of Neisseria meningitidis exhibit translational phase variation via addition or deletion of repetitive coding repeat units within the DNA encoding the protein leader sequence. In contrast, Ope phase variation is the result of transcriptional regulation. Transcription starts 13 nucleotides after the -10 region of an unusual promoter sequence containing a variable number of contiguous cytidine residues and lacking a -35 region. Efficient expression of Ope occurred in strains with 12 to 13 cytidine residues, intermediate expression in strains with 11 or 14 residues and no expression with less than or equal to 10 or greater than or equal to 15 residues. This unusual regulation may have evolved because the Ope protein enables meningococcal invasion and is immunogenic.