Abstract
Two type-II restriction endonucleases, BloI and BloII, have been detected in a Bifidobacterium longum strain. BloI is influenced by dam methylation: it cleaves dam − but not dam + DNA. It shows a temperature and pH optimum of 45°C and pH 7.5. Restriction analysis and cloning experiments showed that the recognition sequence is RGATCY and that the enzyme cuts 5′ to the guanine residue. It is an isoschizomer of commercial enzymes, Bst YI and XhoII. The second activity is not inhibited by dam methylation. It has a temperature optimum between 25°C and 30°C and shows a broad pH optimum between 4.5 and 7.0. The activity is thermolabile and can be heat-killed by a 5 min incubation at 60°C. Cloning and sequencing experiments revealed that its recognition sequence is CTGCAG and that it cuts 5′ to the second guanine residue in the sequence. This enzyme is the first described isoschizomer of PstI.
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