Methylation sensitivity of the restriction enzymes FnuDII and AccII.

The restriction enzymes FnuDII and AccII are isoschizomers of the DNA sequence 5'-CGCG-3'. We have determined that 5-methylcytidine at either cytidine position in this recognition sequence inhibits DNA cleavage by FnuDII and AccII. A third isoschizomer, ThaI was previously shown to exhibit an identical methylation sensitivity. It is remarkable that 3 restriction enzymes derived from diverse microbiological sources exhibit this identical methylation sensitivity.