Identification of a Novel Cryptochrome Differentiating Domain Required for Feedback Repression in Circadian Clock Function *□S

Abstract

Background: Mammalian CRY1 and CRY2 have distinct functions in circadian clock mechanisms. Results: A core domain within the photolyase homology region of CRY1 differentiates CRY1 from CRY2 in clock function. Conclusion: The CRY1/2 differentiating domain is required for strong transcriptional repression and rhythm generation, whereas the divergent tail domain fine tunes clock function. Significance: This study provides novel insights into functional evolution of photolyase/cryptochrome flavoproteins. Circadian clocks in mammals are based on a negative feedback loop in which transcriptional repression by the cryptochromes, CRY1 and CRY2, lies at the heart of the mechanism. Despite similarities in sequence, domain structure, and biochemical activity, they play distinct roles in clock function. However, detailed biochemical studies have not been straightforward and Cry function has not been examined in real clock cells using kinetic measurements. In this study, we demonstrate, through cell-based genetic complementation and realtime molecular recording, that Cry1 alone is able to maintai