Transcription factor (PubMed:17628356). Efficient DNA binding requires dimerization with another bHLH protein, such as cky-1 or ahr-1 (PubMed:17628356, PubMed:9501178). Regulates transcription of target genes, probably acting in complex with cky-1 (PubMed:17628356). Has a role in cellular differentiation (PubMed:9501178, PubMed:15136141). Required for pharyngeal development (PubMed:14757639). In collaboration with ahr-1 it is involved in RMEL/R and SDQR neuron cell migration (PubMed:14757639). Acts in the cellular response to hypoxia (PubMed:11427734). Involved in aggregation behavior by regulating soluble guanylate cyclase gene expression in the URX neurons (PubMed:16919260). Interacts with hif-1 (PubMed:11427734). Heterodimer; efficient DNA binding requires dimerization with another bHLH protein (PubMed:17628356, PubMed:9501178). Forms a heterodimer with ahr-1; binds DNA as heterodimer (PubMed:9501178). Forms a heterodimer with PAS domain-containing protein cky-1; binds DNA as heterodimer (PubMed:17628356). Nuclear location dependent on hif-1 expression in intestinal tissue but not in neuronal cells. Expressed in many cell types throughout development, including hypodermal cells, intestinal cells, pharyngeal cells, and neurons. Expressed in every cell during embryo. Abnormal cell morphology of developing RMEL/R neurons. Arrested development at larvae life stage due to its requirement in the pharynx. Defects in SDQR neuron cell dorsal-ventral migration. Aggregation behavior is diminished. Abolishes guanylate cyclase gene expression in the URX neurons.