They all recognize the same sequence but have different methylation sensitivities. DpnI will only cleave fully-adenomethylated dam sites and hemi-adenomethylated dam sites 60X more slowly. DpnII and MboI share methylation sensitivity and cleave dam sites which lack adenomethylation; each is blocked by complete dam methylation and probably by hemi-methylation as well. Sau3AI will cleave all dam sites regardless of adenomethylation but is completely blocked by methylated cytosines within the dam sequence.