Type II restriction endonucleases are components of prokaryotic DNA restriction-modification mechanisms that protect the organism against invading foreign DNA. These site-specific deoxyribonucleases catalyse the endonucleolytic cleavage of DNA to give specific double-stranded fragments with terminal 5'-phosphates PMID:15770420. This superfamily represents the N-terminal domain of bacterial enzymes similar to type II restriction endonucleases BsuBI and PstI. The structure contains a winged-helix-turn-helix DNA binding structure. The enzymes of the BsuBI restriction/modification (R/M) system recognise the target sequence 5'CTGCAG and are functionally identical with those of the PstI R/M system PMID:1480472. PMID:15770420 PMID:1480472