FULL-LENGTH SEQUENCE-ANALYSIS OF THE VACA GENE FROM CYTOTOXIC AND NONCYTOTOXIC HELICOBACTER-PYLORI

Some clinical isolates of Helicobacter pylori fail to express vacuolat ing cytotoxin, despite possessing a copy of the vacA gene on the chrom osome. To gain insight into the differences between vacA from cytotoxi c and noncytotoxic strains, the vacA open-reading frames from 16 cytot oxic and 22 noncytotoxic strains were sequenced. Mutations that cause truncation of VacA in 11 of 22 noncytotoxic strains were identified, i ncluding internal duplication, large deletion, I-bp insertion, and non -sense mutations, In contrast, none of the 16 cytotoxic strains had an y truncation of VacA, Four cytotoxic strains had inserted sequences do wnstream of vacA. Three were mini-IS605, and the other was a putative rfaJ gene that encodes lipopolysaccharide glucosyltransferase. The rfa J gene identified in this study had a poly(C) tract, resulting in prem ature termination of the gene product. The phylogenetic tree based on the vacA open-reading frame indicated that two different H. pylori lin eages are circulating in Japan and the West.