Myc-Associated Factor X (MAX) is a member of the basic helix-loop-helix leucine zipper (bHLHZ) family of transcription factors. It contains 1 basic helix-loop-helix (bHLH) domain. It is found in the brain, heart, and lung at high levels while lower levels are seen in the liver, kidney, and skeletal muscle. MAX forms a sequence-specific DNA-binding protein complex with MYC or MAD which recognizes the core sequence 5'-CAC[GA]TG-3'. The MYC-MAX complex is a transcriptional activator, whereas the MAD-MAX complex is a repressor. It may repress transcription via the recruitment of a chromatin remodeling complex containing H3 'Lys-9' histone methyltransferase activity.Alternative Names: Protein Max, Class D Basic Helix-Loop-Helix Protein 4, bHLHd4, Myc-Associated Factor X, MAX, BHLHD4