Production of restriction endonucleases using multicopy Hsd plasmids occurring naturally in pathogenic Escherichia coli and Shigella boydii.

A convenient procedure has been devised for detection of restriction endonucleases in the Escherichia coli-Shigella group. With this procedure, two restriction endonucleases, designated Sbo 13 and Eco T22, were found and later were identified as isoschizomers of NruI and AvaIII, respectively. These endonucleases were shown to be produced from small multicopy plasmids. They were isolated from nonpathogenic E. coli into which the plasmids had been introduced by transformation, and purified from contaminating nuclease activity. The yield was high, 1,000 units/g of wet cells for Sbo 13 and 500 units/g for Eco T22. Sbo 13 and Eco T22 should be preferable to NruI and AvaIII because of the high yield and ease in handling the producer cells.