T7 Endonuclease I (T7 Endo I, T7EI), also known as T7 nuclease I in Chinese, can recognize and cleave imperfectly matched DNA, cruciform DNA structures, Holliday junctions ,DNA branch points, and heteroduplex DNA. The cleavage sites are located at the first, second, or third phosphodiester bonds on the 5' side of the mismatch site. Additionally, T7EI can cleave nicked double-stranded DNA, albeit with reduced efficiency. It is noteworthy that T7EI can recognize DNA mismatches resulting from insertions, deletions, or mutations of two or more base pairs (bp) in length, but cannot recognize 1 bp insertions, deletions, or mutations. Furthermore, T7 Endonuclease I does not recognize all types of DNA mismatches and works best with C mismatches. This product is a high-purity protein obtained through cloning and recombinant expression of the T7 Endonuclease I gene in Escherichia coli, followed by purification. It is free of contamination from other endonucleases or exonucleases. (This product is a high-purity protein expressed and purified from E. coli after cloning and expressing the T7 Endonuclease I gene, free from contamination by other endonucleases or exonucleases.)