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, Hpy178III, H...
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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, Hpy178III, Hpy991, and 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 strains, 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 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.
The Hjc protein of Pyrococcus furiosus is an endonuclease that: resolves Holliday junctions, the intermediates in homologous recombination, The amino acid sequence of Hjc is conserved in Archaea, however, it is not-si...
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The Hjc protein of Pyrococcus furiosus is an endonuclease that: resolves Holliday junctions, the intermediates in homologous recombination, The amino acid sequence of Hjc is conserved in Archaea, however, it is not-similar to any of the well-characterized Holliday junction resolvases, In order to investigate the similarity and diversity of the enzymatic properties of Hjc as a Holliday junction resolvase, highly purified Hjc produced in recombinant Escherichia coli was used for detailed: biochemical characterizations. Hjc has specific binding activity to the Holliday-structured DNA, with an apparent dissociation constant (K-d) of 60 nan, The dimeric form of Hjc binds to the substrate DMA. The optimal reaction conditions were determined using a synthetic Holliday junction as substrate, Hjc required a divalent cation for cleavage activity and Mg2+ at 5-10 mM was optimal, Mn2+ could substitute for Mg2+, but it was much less efficient than Mg2+ as the cofactor. The cleavage reaction was stimulated by alkaline pH and KCI at similar to 200 mM, In addition to the high specific activity, Hjc was found to be extremely heat stable, In contrast to the case of Sulfolobus, the Holliday:junction resolving activity detected in *** cell extract thus far is only derived from Hjc.
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