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. MYC/MAX heterodimers bind to target DNA with high affinity. MAX may also form homodimers which recognize the same target sequence, but which are unable to function as transcription activators. Component of some MLL1/MLL complex (By similarity). All four alternatively spliced forms are present during development and in all adult tissues examined. Phosphorylated. Belongs to the MAX family.