Variation of gonococcal lipooligosaccharide structure is due to alterations in poly-G tracts in lgt genes encoding glycosyl transferases

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 alpha chain of the LOS of Neisseria gonorrhaeae are located in a locus containing five genes, IgtA, IgtB, IgtC, IgtD, and IgtE. Sequence analysis showed that IgtA, IgtC, and IgtD cons rained poly-G tracts within the coding frames, leading to the hypothesis that shifts in 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.