DNA methylase

 DNA methylase 

DNA methylase is an enzyme which performs the methylation of DNA. Methylation of DNA is an epigenetic modification which prevents DNA transcription. It does this by binding an extra methyl (CH3) group onto either the cytosine or adenine nucleotide of the DNA sequence. The extra methyl group blocks the the DNA polymerase from reading the strands by creating a conformational change and altering the shape of the DNA, thus changing the expression of the genes. 

A common form of DNA methylation is the 5-methylcytosine (5-mc) which is recognised to be the 5th base of DNA. Within the cell, there is a family of enzymes called DNA methyltransferases which control the activity and rate of DNA methylation.