HMTase(Histone methyltransferases) are histone-modifying enzymes, that catalyze the transfer of one, two, or three methyl teams to lysine and arginine residues of histone proteins. The attachment of methyl groups occurs predominantly at precise lysine or arginine residues on histones H3 and H4. Two major kinds of histone methyltranferases exist, lysine-precise and arginine-precise. In equally varieties of histone methyltransferases, cofactor S-Adenosyl methionine (SAM) serves as a cofactor and methyl donor team. Histone methyltransferase does so by modifying histones at specific internet sites by methylation. Methylation of histones is crucial biologically mainly because it is the principal epigenetic modification of chromatin that decides gene expression, genomic security, stem cell maturation, mobile lineage progress, genetic imprinting, DNA methylation, and mobile mitosis.