A P subtype restriction enzyme that recognizes the double-stranded sequence 5'-CTGCAG-3' and cleaves after A-5. Endonucleolytic cleavage of DNA to give specific double-stranded fragments with terminal 5'-phosphates. Activated by K(+) and Na(+) ions, whereas NH(4)(+) ions appear to inhibit endonuclease activity. Optimum pH is about 9.5. Belongs to the BsuBI/PstI type II restriction endonuclease family.