ANTIGENIC VARIATION IN NEISSERIA-GONORRHOEAE - PRODUCTION OF MULTIPLELIPOOLIGOSACCHARIDES

lndividual cells of Neisseria gonorrhoeae may express a single lipooli gosaccharide (LOS) component on their cell surfaces, or they may simul taneously express multiple LOS structures, Strain FA19 expresses LOS c omponents that react with monoclonal antibodies (MAbs) 2-1-L8 and 1B2. The genetic locus responsible for this phenotype in FA19 was identifi ed by isolating a clone that is able to impart the ability to simultan eously express both LOS molecules to strain 1291, a strain expressing only the MAb 1B2-reactive LOS. This clone, pCLB1, was characterized, a nd the gene responsible for the expression of both LOS components was determined to be lsi2. DNA sequence analysis of lsi2(FA19) indicates t hat there are several differences between the DNA sequences of lsi2(FA 19) and lsi2(1291). The region responsible for the LOS-specific phenot ype 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 lsi2(1291). The polyguanine tra ct in lsi2(FA19) was modified by site-directed mutagenesis to change t he sequence to GGGAGGTGGCGGA to prevent frameshifting during DNA repli cation, transcription, and/or translation, Transformants of strain 129 1 containing this DNA sequence express a single MAb 2-1-L8-reactive LO S component, the same phenotype exhibited by Isi2 defective strains, T hese data indicate that FA19 is able to generate a small amount of fun ctional Lsi2 protein via transcriptional and/or translational frameshi fting, and this limited amount of protein allows for the expression of MAb 1B2-reactive LOS molecules.