Identification of type II restriction and modification systems in Helicobacter pylori reveals their substantial diversity among strains

A total of 22 type II restriction endonucleases with 18 distinct specificit ies have been identified in six Helicobacter pylori strains. Among these 18 specificities are three completely new endonucleases, Hpy178III, Hpy991, a nd Hpy1881, that specifically cleave DNA at TC-NNGA, CCWCG, and TCNGA sites , respectively. The set of endonucleases identified in each strain varies, but ail have four- or five-base recognition sequences. Among 16 H. pylori s trains, examination of the DNA modification status at the recognition sites of 15 restriction endonucleases reveals that each main has a substantially different complement of type II modification systems. We conclude that the type tl restriction-modification systems in H. pylori are highly diverse b etween strains, a unique characteristic of H. pylori. The diverse methylati on status of H. pylori chromosomal DNA may serve as a new typing system to discriminate H. pylori isolates for epidemiological and clinical purposes. This study also demonstrates that H, pylori is a rich source of type II res triction endonucleases.