Binds DNA as a heterodimer with MLX and activates transcription. Binds to the canonical E box sequence 5'-CACGTG-3'. Plays a role in transcriptional activation of glycolytic target genes. Involved in glucose-responsive gene regulation. Efficient DNA binding requires dimerization with another bHLH protein. Binds DNA as a homodimer or a heterodimer with MLX. Predominantly cytoplasmic but shuttles between cytoplasm and nucleus when associated with MLX. Also associates with the outer mitochondrial membrane and may shuttle between the outer mitochondrial membrane and the nucleus. Broadly expressed from 9.5 dpc to at least 15 dpc, with slightly elevated levels in the developing nervous system.