MAX Dimerization Protein 3 (MXD3) belongs to the Myc superfamily of basic helix-loop-helix leucine zipper transcriptional regulators. MXD3 forms a heterodimer with the cofactor MAX that connects specific E-box DNA motifs in the promoters of target genes and regulates their transcription. Disturbance of the MAX-MXD3 complex is correlated with uncontrolled cell proliferation and tumorigenesis. Transcript variants of MXD3 encoding different isoforms have been described.