| Summary: | 碩士 === 國立清華大學 === 生命科學系 === 87 === Helicobacter pylori urease catalyzes hydrolysis of urea to yield the ammonium counterbalance of gastric acid, and is essential for bacteria colonization in gastric lumen. Urease has two structural genes, ureA (about 0.7 kb) and ureB (about 1.7 kb). It is known that there is high divergence of restriction fragment length polymorphism (RFLP) in the ureA-ureB 2.4 kb fragment. In an effort to investigate the ureA-ureB polymorphism of Taiwanese clinical isolates and its relationship with urease activity, 110 strains were characterized by Hae III DNA digestion of the ureA-ureB PCR fragment . Twenty-two RFLPs were found among these isolates, showing a high RFLP divergence. Further Hae III RFLP analysis of the divergence in a 1.2 kb region of ureB gene which consists of urease catalytic center, and a 0.7 kb ureA fragment showed 13 RFLPs and 2 RFLPs, respectively. Sequence analysis of strains from 3 most distinct ureB digest patterns and 2 strains from the most popular ureB RFLP type showed that ureA and ureB sequences were very conservative (amino acid identity > 98%) among these 5 Taiwanese strains. It was noted that there were one amino acid insertion in the N-terminal and two residues deletion in the C-terminal region in the ureA genes of Taiwanese strains as compared with the published ureA sequences. Characterization of 5 chosen Taiwanese strains indicated similar level of specific urease activity (50-80U). In conclusion, despite high RFLP polymorphism in the ureA-ureB region, these two structural genes were well conserved in the amino acid sequence to retain similar level urease activity for its successful colonization in the acidic environment.
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