title: Interaction of circadian clock proteins PER2 and CRY with BMAL1 and CLOCK.
abstract: BACKGROUND
  Circadian oscillation of clock-controlled gene expression is mainly regulated at the transcriptional level. Heterodimers of CLOCK and BMAL1 act as activators of target gene transcription; however, interactions of PER and CRY proteins with the heterodimer abolish its transcriptional activation capacity. PER and CRY are therefore referred to as negative regulators of the circadian clock. To further elucidate the mechanism how positive and negative components of the clock interplay, we characterized the interactions of PER2, CRY1 and CRY2 with BMAL1 and CLOCK using a mammalian two-hybrid system and co-immunoprecipitation assays.
  
  
  RESULTS
  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.
  
  
  CONCLUSIONS
  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.
authors.affiliation: Department of Medicine, Division of Biochemistry, University of Fribourg, Rue du Musée 5, 1700 Fribourg, Switzerland. sonja.langmesser@unifr.ch
authors.forename: Sonja
authors.initials: S
authors.lastname: Langmesser
authors.forename: Tiziano
authors.initials: T
authors.lastname: Tallone
authors.forename: Alain
authors.initials: A
authors.lastname: Bordon
authors.forename: Sandro
authors.initials: S
authors.lastname: Rusconi
authors.forename: Urs
authors.initials: U
authors.lastname: Albrecht
mesh_terms: D056930:ARNTL Transcription Factors; D000818:Animals; D051792:Basic Helix-Loop-Helix Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D001665:Binding Sites; D056926:CLOCK Proteins; D019556:COS Cells; D018797:Cell Cycle Proteins / Q000235:genetics / Q000378:metabolism*; D045744:Cell Line, Tumor; D002522:Chlorocebus aethiops; D002940:Circadian Rhythm; D056931:Cryptochromes; D005420:Flavoproteins / Q000235:genetics / Q000378:metabolism*; D005786:Gene Expression Regulation; D006801:Humans; D051379:Mice; D008954:Models, Biological; D009687:Nuclear Proteins / Q000235:genetics / Q000378:metabolism*; D056950:Period Circadian Proteins; D011485:Protein Binding; D025941:Protein Interaction Mapping; D017434:Protein Structure, Tertiary; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D015534:Trans-Activators / Q000235:genetics / Q000378:metabolism*; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism*
chemical_list: D056930:ARNTL Transcription Factors; D051792:Basic Helix-Loop-Helix Proteins; D056926:CLOCK Proteins; D018797:Cell Cycle Proteins; D056931:Cryptochromes; D005420:Flavoproteins; D009687:Nuclear Proteins; D056950:Period Circadian Proteins; D012333:RNA, Messenger; D015534:Trans-Activators; D014157:Transcription Factors; C538960:BMAL1 protein, human; C538961:Bmal1 protein, mouse; C538963:CRY1 protein, human; C538966:CRY2 protein, human; C538964:Cry1 protein, mouse; C538967:Cry2 protein, mouse; C421902:PER2 protein, human; C513312:Per2 protein, mouse; C538943:CLOCK protein, human; C538944:Clock protein, mouse