Day and Night (image) University of Pennsylvania School of Medicine Share Print E-Mail Caption Schematic of Rev-erb's role in gene expression. At night (left), when Rev-erb concentration decreases, gene expression is turned on by protein complexes that loop the chromosome bringing together distant regions (blue and pink). During the day (right), when Rev-erb levels rise, the protein complexes are kicked out, causing the loop to loosen and turn off gene expression. Credit Yong Kim and Mitch Lazar, Perelman School of Medicine, University of Pennsylvania Usage Restrictions None Share Print E-Mail 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.