Transcription factor (PubMed:17628356). Efficient DNA binding requires dimerization with another bHLH protein, such as ARNT homolog aha-1 (PubMed:17628356). Regulates transcription of target genes, probably acting in complex with aha-1 (PubMed:17628356). Heterodimer; efficient DNA binding requires dimerization with another bHLH protein (PubMed:17628356). Forms a heterodimer with ARNT homolog aha-1; binds DNA as heterodimer (PubMed:17628356).