Duality of CK1D (image) Kyoto University Caption CK1D1 as Mr. Hyde (red) that destabilizes the PER2 protein, and CK1D2 as Dr. Jekyll (blue) that protects PER2. PER2 is represented in the middle. Credit Kyoto University / Jean-Michel Fustin Usage Restrictions None Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.