http://repub.eur.nl/res/aut/11307/ List of Publications en http://repub.eur.nl/static-eur/img/logo.png http://repub.eur.nl http://repub.eur.nl/res/pub/31145/ 2011-08-19T00:00:00Z Despite the sequence and structural conservation between cryptochromes and photolyases, members of the cryptochrome/photolyase (flavo)protein family, their functions are divergent. Whereas photolyases are DNA repair enzymes that use visible light to lesion-specifically remove UV-induced DNA damage, cryptochromes act as photoreceptors and circadian clock proteins. To address the functional diversity of cryptochromes and photolyases, we investigated the effect of ectopically expressed Arabidopsis thaliana (6-4)PP photolyase and Potorous tridactylus CPD-photolyase (close and distant relatives of mammalian cryptochromes, respectively), on the performance of the mammalian cryptochromes in the mammalian circadian clock. Using photolyase transgenic mice, we show that Potorous CPD-photolyase affects the clock by shortening the period of behavioral rhythms. Furthermore, constitutively expressed CPD-photolyase is shown to reduce the amplitude of circadian oscillations in cultured cells and to inhibit CLOCK/BMAL1 driven transcription by interacting with CLOCK. Importantly, we show that Potorous CPD-photolyase can restore the molecular oscillator in the liver of (clock-deficient) Cry1/Cry2 double knockout mice. These data demonstrate that a photolyase can act as a true cryptochrome. These findings shed new light on the importance of the core structure of mammalian cryptochromes in relation to its function in the circadian clock and contribute to our further understanding of the evolution of the cryptochrome/photolyase protein family. http://repub.eur.nl/res/pub/13981/ 2006-03-01T00:00:00Z Cryptochromes (CRYs) are composed of a core domain with structural similarity to photolyase and a distinguishing C-terminal extension. While plant and fly CRYs act as circadian photoreceptors, using the C terminus for light signaling, mammalian CRY1 and CRY2 are integral components of the circadian oscillator. However, the function of their C terminus remains to be resolved. Here, we show that the C-terminal extension of mCRY1 harbors a nuclear localization signal and a putative coiled-coil domain that drive nuclear localization via two independent mechanisms and shift the equilibrium of shuttling mammalian CRY1 (mCRY1)/mammalian PER2 (mPER2) complexes towards the nucleus. Importantly, deletion of the complete C terminus prevents mCRY1 from repressing CLOCK/BMAL1-mediated transcription, whereas a plant photolyase gains this key clock function upon fusion to the last 100 amino acids of the mCRY1 core and its C terminus. Thus, the acquirement of different (species-specific) C termini during evolution not only functionally separated cryptochromes from photolyase but also caused diversity within the cryptochrome family. http://repub.eur.nl/res/pub/13054/ 2002-03-15T00:00:00Z The core oscillator generating circadian rhythms in eukaryotes is composed of transcription--translation-based autoregulatory feedback loops in which clock gene products negatively affect their own expression. A key step in this mechanism involves the periodic nuclear accumulation of clock proteins following their mRNA rhythms after approximately 6 h delay. Nuclear accumulation of mPER2 is promoted by mCRY proteins. Here, using COS7 cells and mCry1/mCry2 double mutant mouse embryonic fibroblasts transiently expressing GFP-tagged (mutant) mPER2, we show that the protein shuttles between nucleus and cytoplasm using functional nuclear localization and nuclear export sequences. Moreover, we provide evidence that mCRY proteins prevent ubiquitylation of mPER2 and subsequent degradation of the latter protein by the proteasome system. Interestingly, mPER2 in turn prevents ubiquitylation and degradation of mCRY proteins. On the basis of these data we propose a model in which shuttling mPER2 is ubiquitylated and degraded by the proteasome unless it is retained in the nucleus by mCRY proteins. http://repub.eur.nl/res/pub/9377/ 2000-01-01T00:00:00Z Nuclear entry of circadian oscillatory gene products is a key step for the generation of a 24-hr cycle of the biological clock. We have examined nuclear import of clock proteins of the mammalian period gene family and the effect of serum shock, which induces a synchronous clock in cultured cells. Previously, mCRY1 and mCRY2 have been found to complex with PER proteins leading to nuclear import. Here we report that nuclear translocation of mPER1 and mPER2 (1) involves physical interactions with mPER3, (2) is accelerated by serum treatment, and (3) still occurs in mCry1/mCry2 double-deficient cells lacking a functional biological clock. Moreover, nuclear localization of endogenous mPER1 was observed in cultured mCry1/mCry2 double-deficient cells as well as in the liver and the suprachiasmatic nuclei (SCN) of mCry1/mCry2 double-mutant mice. This indicates that nuclear translocation of at least mPER1 also can occur under physiological conditions (i.e., in the intact mouse) in the absence of any CRY protein. The mPER3 amino acid sequence predicts the presence of a cytoplasmic localization domain (CLD) and a nuclear localization signal (NLS). Deletion analysis suggests that the interplay of the CLD and NLS proposed to regulate nuclear entry of PER in Drosophila is conserved in mammals, but with the novel twist that mPER3 can act as the dimerizing partner.