SacNI, an isoschizomer of the restriction endonuclease, BanII [Sugisaki et al., Nucleic Acids Res. 10 (1982) 5747-5752], has been isolated from Streptomyces achromogenes N-J-H. SacNI recognizes the palindromic sequence, 5 -GRGCY/C, and cleaves within the recognition sequence, generating a 3 protruding RGCY end (where R = A or G, and Y = C or G).