Transcriptional repressor. MXI1 binds with MAX to form a sequence-specific DNA-binding protein complex which recognizes the core sequence 5'-CAC[GA]TG-3'. MXI1 thus antagonizes MYC transcriptional activity by competing for MAX. Interacts with SMC3 (By similarity). Efficient DNA binding requires dimerization with another bHLH protein. Binds DNA as a heterodimer with MAX. Interacts with RNF17 (By similarity). High levels found in the brain, heart and lung while lower levels are seen in the liver, kidney and skeletal muscle. Disease susceptibility is associated with variants affecting the gene represented in this entry.