A novel endonuclease specified by bacteriophage lambda. Purification and properties of the enzyme

A DNA endonuclease whose expression is under the control of the b region of bacteriophage lambda has been partially purified from an induced lambda lysogen. In a reaction that requires single-stranded DNA, ATP, and Mg2+, the lambda-induced endonuclease makes one double strand break in pBR322 and other covalently closed circular DNA molecules, converting these substrates into unit-length linear forms. The double strand break in pBR322 DNA occurs at one of several preferred sites. Linear DNA appears not to be a good substrate for the enzyme.