T7 Endonuclease I (T7E1) recognizes and cleaves non-perfectly matched DNA, cruciform DNA structures, Holliday structures or junctions, hetero duplex DNA and more slowly, nicked double-stranded DNA. The cleavage site is at the first, second or third phosphodiester bond that is 5´ to the mismatch. The protein is the product of T7 gene 3. GenCrispr T7 Endonuclease I is a fusion protein produced from E.coli.