Figure 3.

Effect of CRY1 or PER2 nuclear entry on E-box binding and transcription in the Cry1/2^−/−; Per1/2^-/ mutant. (A) Repressor protein expression in wild-type and mutant mouse cell lines analyzed by immunoblotting. (B) 4-OHT-induced nuclear entry of CRY1–ER* and PER2–ER* in the quadruple mutant cell line analyzed by immunofluorescence microscopy. (C–F) Effects of CRY1 or PER2 nuclear entry on CLOCK–BMAL1 function: CRY1–ER* nuclear entry inhibits transcription (C) without displacing CLOCK–BMAL1 from the promoter (D). In the absence of CRYs, PER2–ER* nuclear entry does not affect E-box transcription (E) or CLOCK–BMAL1 binding to the E-box (F). (EtOH) Ethanol.