MAX Dimerization Protein 1 (MXD1)

The MAD and MXI1 genes encode proteins that belong to a distinct subfamily of MAX -interacting proteins. The MAX protein specifically interacts with the MYC protein family by forming heterodimers mediated by their basic-helix-loop-helix-leucine zipper (bHLHZ) interaction domains. Binding to MAX is essential for MYC transcription and transforming activity; MYC homodimers are inactive. Both MAD and MXI1 bind MAX in vitro, forming a sequence-specific DNA-binding complex similar to the MYC-MAX heterodimer. MAD and MYC compete for binding to MAX. In addition, MAD acts as a transcriptional repressor, while MYC appears to function as an activator. MXI1 also appears to lack a transcriptional activation domain. Therefore, MXI1 and MAD might antagonize MYC function and are candidate tumor suppressor genes