MYC associated factor X contains 1 basic helix-loop-helix (bHLH) domain and belongs to the MAX family. It is highly expressed in the brain, heart, and lung while lower levels are seen in the liver, kidney, and skeletal muscle. MYC associated factor X can form homodimers and heterodimers with other family members, which include Mad, Mxi1, and Myc. Myc is an oncoprotein implicated in cell proliferation, differentiation, and apoptosis. The homodimers and heterodimers compete for a common DNA target site (the E box) and rearrangement among these dimer forms provides a complex system of transcriptional regulation. MYC associated factor X may also repress transcription via the recruitment of a chromatin remodeling complex containing H3 'Lys-9' histone methyltransferase activity. Multiple alternatively spliced transcript variants have been described for MYC associated factor X gene but the full-length nature for some of them is unknown.