Does not bind DNA itself but suppresses both HES1-mediated N box-dependent transcriptional repression and binding of HES1 to E box sequences. Also suppresses HES1-mediated inhibition of the heterodimer formed by ASCL1/MASH1 and TCF3/E47, allowing ASCL1 and TCF3 to up-regulate transcription in its presence. Promotes cell differentiation. Transcription repression requires formation of a complex with a corepressor protein of the Groucho/TLE family (By similarity). Interacts with HES1. Expressed in both undifferentiated and differentiated cells. High levels of expression are observed in several embryonic tissues including the nervous system, muscle and thymus. In the nervous system, initially expressed in the closing neural tube, then in the spinal cord, cranial and dorsal root ganglia, and brain neuroepithelium. Also expressed in epithelial cells of the embryonic respiratory, urinary and digestive systems. In the limb buds, expressed in skeletal muscle and presumptive tendons. Expressed in both embryo and adult. Expression in the embryo is detected from 8.5 dpc. In the retina, expressed at high levels at postnatal 0 dpc. Expression in brain and retina decreases postnatally but still detectable in adult. The C-terminal WRPW motif is a transcriptional repression domain necessary for the interaction with Groucho/TLE family members, transcriptional corepressors recruited to specific target DNA by Hairy-related proteins. Has a particular type of basic domain (presence of a helix-interrupting proline) that binds to the N-box (CACNAG), rather than the canonical E-box (CANNTG).