Mammalian cells generate molecular ~24-hour rhythms using a multi-protein complex that eventually negatively regulates the expression of its components. Since the dynamics of this mechanism is poorly understood, we propose to study: (i) the role of transportin1-mediated nuclear transport using FRAP and interaction experiments; (ii) the role of  COPI vesicles for module assembly using FRET, co-immunoprecipitation and mass spectrometry; and (iii) the identity and dynamics of module composition using quantitative mass spectrometry and subsequent functional analyses.