Component of a transcriptional repressor complex together with MAX (PubMed:8425218). In complex with MAX binds to the core DNA sequence 5'-CAC[GA]TG-3' (PubMed:8425218). Antagonizes MYC transcriptional activity by competing with MYC for MAX binding (PubMed:8425218). Binds to the TERT promoter and represses telomerase expression, possibly by interfering with MYC binding (PubMed:12837246). Heterodimer with MAX; the interaction is required for DNA-binding (PubMed:8425218). DNA binding requires dimerization with another bHLH protein; does not form homodimers, and does not bind to DNA in the absence of MAX in vitro (PubMed:8425218). Interacts with RNF17 (By similarity). Ubiquitinated by BIRC2/c-IAP1, leading to its subsequent degradation by the proteasome.