McrBC specifically cleaves DNA containing methyl cytosine (mC : 5-hydroxymethylcytosine, 5-methylcytosine, 4-methylcytosine) preceded by a purine nucleotide (Pu: A or G). DNA cleavage by McrBC requires at least two PumC sites within a distance of 40–2,000 bp.  McrBC requires GTP for cleavage.