Interaction of circadian clock proteins PER2 and CRY with BMAL1 and CLOCK

Both PER2 and the CRY proteins were found to interact with BMAL1 whereas only PER2 interacts with CLOCK. CRY proteins seem to have a higher affinity to BMAL1 than PER2. Moreover, we provide evidence that PER2, CRY1 and CRY2 bind to different domains in the BMAL1 protein.The regulators of clock-controlled transcription PER2, CRY1 and CRY2 differ in their capacity to interact with each single component of the BMAL1-CLOCK heterodimer and, in the case of BMAL1, also in their interaction sites. Our data supports the hypothesis that CRY proteins, especially CRY1, are stronger repressors than PER proteins.Circadian rhythms are recurring fluctuations with a period of about 24 hours that can be observed in the physiology and behavior of most living organisms from cyanobacteria to humans [1]. They are controlled by an autonomous circadian clock, which can be synchronized to the environmental day-night cycle. In mammals, the suprachiasmatic nucleus (SCN), a structure in the ventral part of the hypothalamus, appears to be the main coordinator of the circadian timing system [2,3] synchronizing peripheral clocks present in all tissues throughout the body [4].The oscillatory mechanism underlying the circadian clock has been unraveled by means of genetic analysis in Drosophila and mammals [5]. In the latter, a heterodimeric complex of two transcriptional activators, CLOCK and BMAL1, binds to E-box enhancer elements present in the promoters of target genes and thereby activates the expression of three Period (Per1, Per2 and Per3) and two Cryptochrome genes (Cry1 and Cry2). PER and CRY proteins translocate to the nucleus where CRY proteins act as potent (and PER proteins as mild) inhibitors of CLOCK-BMAL1-induced transcription [6,7]. The positive (CLOCK-BMAL1) and negative (CRY, PER) arms of the feedback loop are coupled via the nuclear orphan receptor REV-ERBα [8] generating a stabilized feedback loop that drives recurrent rhythms in mRNA and protein levels of clock components.Trans