MAD/MXI1

**Semantic type:** Amino Acid, Peptide, or Protein

**Definition:** MAD and MXI1 bZIP proteins belong to a subfamily of MAX-interacting proteins. MAX interacts with MYC via bZIP interaction domains and MAX binding is essential for MYC activity; MYC homodimers are inactive. MAD/MAX and MXI1/MAX heterodimers form a DNA-binding complex similar to MYC/MAX. MAD and MXI1 act as transcriptional repressors and appear to antagonize MYC by competing for MAX, and for DNA binding sites, and recruit SIN3 proteins and their associated co-repressors. (from OMIM 600021, 600020, and NCI)