Transcription regulator. 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 (By similarity). Efficient DNA binding requires dimerization with another bHLH protein. Binds DNA as a heterodimer with MYC or MAD. Component of some MLL1/MLL complex (By similarity). High levels are seen in the kidney, gills and uterus. It is also found in the brain and heart. Expressed at relatively constant levels up to the end of the embryonic stage (72 hours), with a moderate decrease between the 12 and 24 hours stages marked by the formation of somites and organ rudiments. Phosphorylated. Belongs to the MAX family.