A specific endonuclease, Sau 3AI, has been partially purified from Staphylococcus aureus strain 3A by DEAE-cellulose chromatography. The enzyme cleaves adenovirus type 5 DNA many times, SV40 DNA eight times but does not cleave double-stranded phi X174 DNA. It recognizes the sequence (see article) and cleaves as indicated by the arrows. Evidence is presented that this enzyme plays a role in the biological restriction-modification system of Staphylococcus aureus strain 3A.

The occurrence of class II restriction endonucleases (enzymes that both recognize and cleave a specific nucleotide sequence in deoxyribonucleic acid [DNA]) in Staphylococcus aureus has been investigated by analysis of crude extracts obtained from different propagating strains of the International Phage Typing System. Of the four main groups of strains in the International System, only extracts of group II strains were found to contain class II restriction endonucleases. The identical cleavage patterns obtained by incubation of different DNAs with cell extracts of group II strains suggest that these enzymes all recognize and cleave the same nucleotide sequence. This recognition site has been determined to be 5-G-AT -C-3' for the prototype of these enzymes, Sau3AI (J. S. 3'-C-T-A-G-5'fothprttpofteeezmsSuAI(.. Sussenbach et al., Nucleic Acids Res. 3:3192-3202, 1976). Evidence is presented that the classification of group II strains is based on restriction modification and is correlated with the presence of a class II restriction endonuclease that recognizes and cleaves the above sequence.