Transcription factor that binds to the immunoglobulin enhancer Mu-E5/KE5-motif. Involved in the initiation of neuronal differentiation. Activates transcription by binding to the E box (5'-CANNTG-3'). Isoform 2 inhibits MYOD1 activation of the cardiac alpha-actin promoter. Binds to the E-box present in the somatostatin receptor 2 initiator element (SSTR2-INR) to activate transcription. May have a regulatory function in developmental processes as well as during neuronal plasticity. Efficient DNA binding requires dimerization with another bHLH protein. Isoform 2 seems to form inactive heterodimers with MYOD1. Interacts with HIVEP2. Interacts with NEUROD2. Interacts with AGBL1 (By similarity). Interacts with BHLHA9. Expressed in the cerebral cortex, Purkinje and granule cell layers of the cerebellum, olfactory neuroepithelium, pyramidal cells of hippocampal layers CA1-CA4, and in the granular cells of the dentate gyrus. Expressed in proliferative zones during development and in the adult in areas of neuronal plasticity. At 12 dpc, expression is localized in the cortex, cerebellum, pons, medulla and spinal cord. From 18 dpc to adulthood, high levels of expression are found in the pyramidal cells of hippocampal layers CA1-CA4, and in the granular cells of the dentate gyrus. At postnatal day 7, expression is high in the visual cortex and in the subependymal region extending from the anterior lateral ventricle into the olfactory bulb.