5-methyl cytosine mutation of DNA (DNA methylation) leads to:

A i.e. Deamination to thiamine; B i.e. DNA repair > C i.e. Methylation protects the host DNA from cleavage by its own restriction enzymeDeamination of cytosine forms uracil and deamination of 5 methyl cytosine forms thymine. TDG & MBD4 DNA uracil glycosylase remove either U or T residues paired with G, generated by deamination.DNA methylation of adenine at 5' GATC repair mismatched base pairs. And methylated parental (template) strand is protected from cleavage / digestion by its own restriction enzyme.