c-fos CRE-binding activity of CREB/ATF family in the SCN is regulated by light but not a circadian clock.

The DNA-binding activity of cAMP-responsive element binding protein (CREB) in the suprachiasmatic nucleus (SCN) was examined with Ca or cAMP-responsive element (Ca/CRE) in upstream sequence of c-fos gene using electro-mobility shift assay (EMSA). By using supershift assay, Ca/CRE-binding activity in the SCN was shown to contain not only CREB but also activating transcription factor-1 (ATF-1). Furthermore, photic-induction of CREB binding activity to Ca/CRE in the SCN occurred at all circadian times tested, indicating that CREB DNA-binding in the SCN was not gated by the endogenous clock. These results implicated the role of CREB/ATF family in photic neuronal signaling in the SCN.