title: Nuclear entry mechanism of rat PER2 (rPER2): role of rPER2 in nuclear localization of CRY protein.
abstract: Mammalian PERIOD2 protein (PER2) is the product of a clock gene that controls circadian rhythms, because PER2-deficient mice have an arrhythmic phenotype. The nuclear entry regulation of clock gene products is a key step in proper circadian rhythm formation in both Drosophila and mammals, because the periodic transcription of clock genes is controlled by an intracellular, oscillating, negative feedback loop. The present study used deletion mutants of rat PER2 (rPER2) to identify the functional nuclear localization signal (NLS) in rPER2. The elimination of putative NLS (residues 778 to 794) from the rPER2 fragment resulted in the loss of nuclear entry activity. Adding the NLS to the cytosolic protein (bacterial alkaline phosphatase) translocates the fusion protein to the nuclei. The data indicate the presence of a functional NLS in rPER2. Furthermore, intact rPER2 was preferentially translocated from the cytoplasm to the nucleus when coexpressed with human CRY1 (hCRY1). However, rPER2 mutants lacking a carboxyl-terminal domain could not enter the nucleus even in the presence of hCRY1. In addition, coexpression of the nuclear localization domain (residues 512 to 794) lacking rPER2 and CRY1 changed the subcellular localization of CRY1 from the nucleus to the cytoplasm. In vitro protein interaction studies demonstrated that the carboxyl-terminal domain of rPER2 is essential for binding to CRY1. The data suggested that both the rPER2 NLS and carboxyl-terminal CRY binding domain are essential for nuclear entry of the rPER2-CRY1 complex.
authors.affiliation: Clock Cell Biology Group, Institute of Molecular and Cell Biology, National Institute of Advanced Industrial Science and Technology, Tsukuba, Ibaraki 305-8566, Japan.
authors.forename: K
authors.initials: K
authors.lastname: Miyazaki
authors.forename: M
authors.initials: M
authors.lastname: Mesaki
authors.forename: N
authors.initials: N
authors.lastname: Ishida
mesh_terms: D021581:Active Transport, Cell Nucleus; D000818:Animals; D001665:Binding Sites; D019556:COS Cells; D018797:Cell Cycle Proteins; D002467:Cell Nucleus / Q000378:metabolism; D056931:Cryptochromes; D029721:Drosophila Proteins; D005136:Eye Proteins; D005420:Flavoproteins / Q000378:metabolism*; D006801:Humans; D019913:Nuclear Localization Signals; D009687:Nuclear Proteins / Q000235:genetics / Q000378:metabolism* / Q000502:physiology*; D056950:Period Circadian Proteins; D017956:Photoreceptor Cells, Invertebrate; D017434:Protein Structure, Tertiary; D051381:Rats; D043562:Receptors, G-Protein-Coupled; D017384:Sequence Deletion; D014157:Transcription Factors; D014162:Transfection
chemical_list: C538963:CRY1 protein, human; D018797:Cell Cycle Proteins; C538964:Cry1 protein, mouse; C538965:Cry1 protein, rat; D056931:Cryptochromes; D029721:Drosophila Proteins; D005136:Eye Proteins; D005420:Flavoproteins; D019913:Nuclear Localization Signals; D009687:Nuclear Proteins; C421902:PER2 protein, human; C513311:Per2 protein, rat; D056950:Period Circadian Proteins; D043562:Receptors, G-Protein-Coupled; D014157:Transcription Factors; C119828:cry protein, Drosophila