sentences:  The NPAS2 protein is a member of the basic helix-loop-helix (bHLH)-PAS transcription factor family and is expressed in the SCN.NPAS2 is a PAS domain-containing protein, which binds other proteins via their own protein-protein (PAS) binding domains.Like its paralogue, CLOCK (another PAS domain-containing protein), the NPAS2 protein can dimerize with the BMAL1 protein and engage in a transcription/translation negative feedback loop (TTFL) to activate transcription of the mammalian "Per" and "Cry" core clock genes.