ANALYSES OF THE CAG PATHOGENICITY ISLAND OF HELICOBACTER-PYLORI

Most strains of Helicobacter pylori from patients with peptic ulcer di sease or intestinal-type gastric cancer carry cagA, a gene that encode s an immunodominant protein of unknown function, whereas many of the s trains from asymptomatically infected persons lack this gene. Recent s tudies showed that the cagA gene lies near the right end of a approxim ate to 37 kb DNA segment (a pathogenicity island, or PAI) that is uniq ue to cagA(+) strains and that the cag PAI was split in half by a tran sposable element insertion in the reference strain NCTC11638. In compl ementary experiments reported here, we also found the same cag PAI, an d sequenced a 39 kb cosmid clone containing the left 'cagII' half of t his PAI. Encoded in cagll were four proteins each with homology to fou r components of multiprotein complexes of Bordetella pertussis ('PtI') , Agrobacterium tumefaciens ('Vir'), and conjugative plasmids ('Tra') that help deliver pertussis toxin and T (tumour inducing) and plasmid DNA, respectively, to target eukaryotic or prokaryotic cells, and also homologues of eukaryotic proteins that are involved in cytoskeletal s tructure. To the left of cagll in this cosmid were genes for homologue s of HsIU (heat-shock protein) and Era (essential GTPase); to the righ t of cagll were homologues of genes for a type I restriction endonucle ase and ion transport functions. Deletion of the cag PAI had no effect on synthesis of the vacuolating cytotoxin, but this deletion and seve ral cag insertion mutations blocked induction of synthesis of proinfla mmatory cytokine IL-8 in gastric epithelial cells. Comparisons among H . pylori strains indicated that cag PAI gene content and arrangement a re rather well conserved. We also identified two genome rearrangements with end-points in the cag PAI, One, in reference strain NCTC11638, i nvolved IS605, a recently described transposable element (as also foun d by others). Another rearrangement, in 3 of 10 strains tested (includ ing type strain NCTC11637), separated the normally adjacent cagA and p icA genes and did not involve IS605. Our results are discussed in term s of how cag-encoded proteins might help trigger the damaging inflamma tory responses in the gastric epithelium and possible contributions of DNA rearrangements to genome evolution.