Plays a role in controlling the transcriptional activity of MyoD, ensuring that expanding myoblast populations remain undifferentiated. Repression may occur through muscle-specific E-box occupancy by homodimers. May also negatively regulate bHLH-mediated transcription through an N-terminal repressor domain. Serves as a key regulator of acinar cell function, stability, and identity. Also required for normal organelle localization in exocrine cells and for mitochondrial calcium ion transport. May function as a unique regulator of gene expression in several different embryonic and postnatal cell lineages. Binds to the E-box consensus sequence 5'-CANNTG-3' (By similarity). Forms homodimers or heterodimers with TCF3 gene products E12 and E47. These dimers bind to the E-box site, however, heterodimer with MYOD1 does not bind target DNA. Expressed in liver, spleen and olfactory epithelium. Weaker expression is seen in skeletal muscle, cardiac muscle, eye and brain tissue. Lacks a classic transcription activation domain and instead possesses an N-terminal region capable of inhibiting heterologous activators.