Dnmt3a belongs to the mammalian methyltransferase gene family which is responsible for tissue-specific gene expression. Dnmt3a together with other methyltransferases conducts de novo methylation of cytosine residues in CpG islands by the enzymatic addition of methyl residues from S-adenosyl-L-methionine to the 5-carbon atom of the cytosine ring. Dnmt3a also directs a metabolic program by repressing key genes to enable the coupling of insulin secretion to glucose levels during beta cell maturation. Loss of Dnmt3a in pancreatic beta cells prevents this developmental metabolic reprogramming, resulting in loss of GSIS (Glucose-Stimulated Insulin Secretion)). Dnmt3a overexpression has been found in several cancers including AML (Acute Myeloid Leukemia).