Variation o f Gonococca l Lipooligosaccharide Structure Is Due to Alterations in Poly - G Tracts in lgt Genes Encoding

The lipooligosaccharide (LOS) expressed by gonococci spontaneously varies its structure at high frequency, but the underlying genetic mechanism has not been described. We have previously reported that the genes encoding the glycosyl transferases responsible for the biosynthesis of the variable o~ chain of the LOS of Neisseria gonorrhoeae are located in a locus containing five genes, lgtA, lgtB, IgtC, IgtD, and lgtE. Sequence analysis showed that tgtA, lgtC, and IgtD contained poly-G tracts within the coding frames, leading to the hypothesis that shiftsin the number of guanosine residues in the poly-G tracts might be responsible for the.high frequency variation in structure of gonococcal LOS. We now provide experimental evidence confirming this hypothesis.