Chromatin domains rich in inheritance

Only certain histone posttranslational modifications qualify as being epigenetic Epigenetic phenomena are heritable changes to gene expression that occur without changes to the DNA sequence and that include posttranslational modifications (PTMs) to the histones that package DNA into chromatin. These PTMs are deposited on histones by enzymes in response to an “initiator,” ultimately altering chromatin structure and, accordingly, gene expression. In multicellular organisms, cellular identity is established by master regulators (initiators) that can activate or repress transcription through their sequence-specific DNA binding activity. The accurate transmission of distinct gene expression profiles during cell division is essential for preserving the properties of cell lineages. Thus, a key feature of the epigenetic process is that after the initiator subsides, these informative chromatin PTMs must be inherited by subsequent cell generations. Numerous histone PTMs can occur, but can they all convey epigenetic information? We discuss the few histone PTMs that qualify as epigenetic and the distinct features of the enzymes that deposit them that account for their epigenetic status.