Caption

Methyltransferase and DNA. Molecular model of the enzyme HhaI methyltransferase (purple) complexed with a molecule of DNA (deoxyribonucleic acid, yellow and green). Methyltransferases are enzymes that catalyse the transfer of methyl groups (CH3) to DNA nucleotides. HhaI methyltransferase catalyses the transfer to cytosine nucleotides. Methylation of the nucleotides modulates gene expression.