Members of the bHLH-PAS family are transcription factors that contain a basic helix-loop-helix (bHLH) DNA-recognition motif which is located N-terminal to a PAS domain comprised of two imperfect direct repeats. Human NPAS1 is a deduced 590-amino acid protein which shares 86% sequence homology with mouse Npas1. In order for NPAS1 to bind DNA efficiently, it must form a dimer with another bHLH protein. NPAS1 interacts with ARNT (aryl hydrocarbon receptor nuclear translocator), and shows predominant expression in brain tissue. NPAS1 is also implicated in the control of regulatory pathways relevant to schizophrenia and to psychotic illness, and may play a role in late central nervous system development by modulating EPO expression in response to cellular oxygen levels.