Transcriptional regulator. Involved in the initiation of neuronal differentiation. Activates transcription by binding to the E box (5'-CANNTG-3') (By similarity). Efficient DNA binding requires dimerization with another bHLH protein. Forms homo- or heterooligomers with myogenin, E12 and ITF2 proteins. Interacts with PTF1. Interacts with RUNX1T1. Interacts with NEUROD2 (By similarity). Interacts with BHLHA9. Additional isoforms seem to exist. Isoform gamma is highly expressed in lung, kidney, spleen, and is expressed at reduced levels in heart, muscle, liver, pituitary, brain and the trigeminal ganglion. The expression of isoform alpha predominates over isoform gamma in the pituitary and the brain.