Plays a role in controlling the transcriptional activity of MyoD, ensuring that expanding myoblast populations remain undifferentiated (PubMed:17612490). 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'. 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 pancreatic tissue only in acinar cells. There is a complete absence of expression in intra- or interlobular pancreatic ducts and in all islet cells. First observed at 10.5 dpc in the primitive gut and in the developing lung bud. Expression in the gut persists through 16.5 dpc and remains restricted primarily to the epithelial lining of the esophagus, stomach and intestine. Expression in the lung is detected in the bronchial epithelium at 14.5 dpc and at 15.5 dpc. Expressed specifically in acinar cells during pancreatic development. Detected in skeletal muscle tissues beginning at 12.5 dpc, persisting throughout all embryonic stages examined although, in older embryos expression becomes severely reduced. Up-regulated by XBP1. Induced by chemical activators of the unfolded protein response (UPR) such as tunicamycin and thapsigargin, and also by glucose starvation (PubMed:17612490). Lacks a classic transcription activation domain and instead possesses an N-terminal region capable of inhibiting heterologous activators. Mice display incorrect granule organization in pancreatic acinar cells and other serous exocrine cells such as parotid acini and gastric chief cells. They also display mislocalization of mitochondria and Golgi apparatus and reduced Ca(2+) uptake by mitochondria.