Antigenic variation in Neisseria gonorrhoeae: Production of multiple lipooligosaccharides

Individual cells of Neisseria gonorrhoeae may express a single lipooligosaccharide (LOS) component on their cell surfaces, or they may simultaneously express multiple LOS structures. Strain FA19 expresses LOS components that react with monoclonal antibodies (MAbs) 2-1-L8 and 1B2. The genetic locus responsible for this phenotype in FA19 was identified by isolating a clone that is able to import the ability to simultaneously express both LOS molecules to strain 1291, a strain expressing only the MAb 1B2-reactive LOS. This clone, pCLB1, was characterized, and the gene responsible for the expression of both LOS components was determined to be Isi2. DNA sequence analysis of lsi2(FA19) indicates that there are several differences between the DNA sequences of lsi2(FA19) and Isi2₁₂₉₁. The region responsible for the LOS-specific phenotype change in lsi2(FA19) was identified by deletion and transformation analysis, mapping to a polyguanine tract within lsi2 where lsi2(FA19) possesses a +2 frameshift relative to lsi2₁₂₉₁. The polyguanine tract in lsi2(FA19) was modified by site- directed mutagenesis to change the sequence to GGGAGGTGGCGGA to prevent frameshifting during DNA replication, transcription, and/or translation. Transformants of strain 1291 containing this DNA sequence express a single MAb 2-1-LB-reactive LOS component, the same phenotype exhibited by lsi2- defective strains. These data indicate that FA19 is able to generate a small amount of functional Lsi2 protein via transcriptional and/or translational frameshifting, and this limited amount of protein allows for the expression of MAb 1B2-reactive LOS molecules.