5-methylcytosine mutation of DNA (DNA methylation) leads to
Deamination to thymine
DNA repair
Methylation protects the host DNA from cleavage by its own restriction enzyme
All of these
DNA methylation is essential for enthralling a number of the cellular process including transcription, genomic imprinting, developmental regulation, mutagenesis, DNA repair and chromatin organization.
DNA methylation also protects DNA from bacteria's own restriction enzymes.
Deamination of 5-methylcytosine forms thymine, this can result in transition mutation.