The effect of HhaI methylation on DNA local structure.

The effect of methylating the central cytosine in the sequence GCGC on the sensitivity to digestion by deoxyribonuclease I was investigated. Examination of five such sites shows that the extra methyl group renders the bond on its 5' side more susceptible to cleavage, and this is interpreted by suggesting that it causes small changes in the local DNA phosphate orientation.