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Background
MAX(Max protein), also called Myc-associated factor x, is the most conserved dimerization component of the MYC-MAX-MXD1 network of basic helix-loop-helix leucine zipper (bHLHZ) transcription factors that regulate cell proliferation, differentiation, and apoptosis. The conservation of the MAX sequence is particularly high in the bHLHZ domain, which is involved in protein-protein interactions and DNA binding. The MAX gene is located on chromosome 14q23 by fluorescence in situ chromosomal hybridization. Both quasisymmetric heterodimers resemble the symmetric MAX homodimer, albeit with marked structural differences in the coiled-coil leucine zipper regions that explain preferential homo- and heteromeric dimerization of these 3 evolutionarily related DNA-binding proteins. MAX acts as a classic tumor suppressor gene. Normal lymphocytes from patients showed absence of methylation of the MAX promoter and biallelic expression of MAX, which ruled out an imprinting-mediated effect on MAX expression. The ability of these cells to divide, differentiate, and apoptose in the absence of Max demonstrated for the first time that these processes can occur via Max- and possibly Myc-independent mechanisms.