High Quality Content by WIKIPEDIA articles! NPAS3 or Neuronal PAS domain protein 3 is a brain-enriched transcription factor belonging to the bHLH-PAS superfamily of transcription factors, the members of which carry out diverse functions, including circadian oscillations, neurogenesis, toxin metabolism, hypoxia, and tracheal development. NPAS3 contains basic-helix-loop-helix structural motif and PAS domain, like the other proteins in the superfamily.