Methyltransferases are enzymes that transfer a methyl group (–CH₃) from a donor molecule, usually S-adenosylmethionine (SAM), to specific substrates, including DNA, RNA, and proteins. This process is crucial for various biological functions, such as gene regulation, protein function, and cellular signaling. These enzymes play a significant role in epigenetics, where they can modify DNA and affect gene expression without altering the underlying genetic code. Methylation patterns established by methyltransferases can influence development, differentiation, and disease processes, including cancer.