Abstract
A total of 22 type II restriction endonucleases with 18 distinct specificities have been identified in six
Helicobacter pylori
strains. Among these 18 specificities are three completely new endonucleases,
Hpy
178III,
Hpy
99I, and
Hpy
188I, that specifically cleave DNA at TCNNGA, CGWCG, and TCNGA sites, respectively. The set of endonucleases identified in each strain varies, but all have four- or five-base recognition sequences. Among 16
H. pylori
strains, examination of the DNA modification status at the recognition sites of 15 restriction endonucleases reveals that each strain has a substantially different complement of type II modification systems. We conclude that the type II restriction-modification systems in
H. pylori
are highly diverse between strains, a unique characteristic of
H. pylori
. The diverse methylation 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 restriction endonucleases.