Epigenetic writers function as regulators of gene expression, carrying out precise modifications to DNA and histones. More specifically, these writers are enzymes that add small chemical tags such as acetyl and methyl groups via covalent bonding. Some examples of epigenetic writers include HMTs and HATs. HMTs add methyl groups to histones while HATS add acetyl groups. These enzymes act on chromatin and their modifications influence various cellular processes without altering the underlying DNA sequence. Epigenetic writers carry out these rapid modifications in response to environmental cues.