The EP400 gene encodes a subunit of the NuA4 histone acetyltransferase (HAT) complex, which is responsible for carrying out the acetylation of the nucleosomal histones H2A and H4. This modification is believed to help activate the transcription of certain genes, presumably by altering nucleosome-DNA interactions and promoting the association of the modified histones with other transcription-regulating proteins. Genes suspected to be targeted for transcriptional activation by this complex include E2F1 and MYC during cellular proliferation as well as ZNF42. While EP400 is ubiquitously expressed, overexpression of the gene is seen in peripheral blood mononuclear cells, CD8 T-cells, lymph node, B lymphocytes and placenta.