Ceriani, M.F., Darlington, T.K., Staknis, D., Mas, P., Petti, A.A., Weitz, C.J., Kay, S.A.
Notes: Most organisms display an endogenous timekeeping mechanism, or circadian clock, which consists of negative feedback loops of gene regulation that facilitate adaptation to cycles of light and darkness. In Drosophila, as well as other organisms, several of the molecules involved in sustaining this circadian clock have been identified. A gene product required for circadian photoreception has recently been identified in Drosophila, and termed crytochrome (CRY). These researchers investigated whether CRY could interact directly with the core clock proteins PERIOD (per) and TIMELESS (tim). The Drosophila cell line S2 was transiently transfected with a firefly luciferase reporter construct under control of the tim promoter, in conjunction with different combinations of constructs expressing clk, per, tim, and cry. Data was normalized to a cotransfected reporter plasmid, either the pRL-null Vector, a Renilla luciferase vector, or a beta-galactosidase expression vector, and the resulting activities measured using either the Dual-Luciferase® Reporter Assay System or the Beta-Galactosidase Enzyme Assay System. These transfection studies, along with coimmuneprecipitation assays, a yeast two-hybrid assay, and immunolocalization studies, show that CRY can block the function of PER/TIM heterodimeric complexes in a light-dependent fashion. In addition, PER/TIM and CRY influence the subcellular distribution of these protein complexes. Thus, CRY acts as a circadian photoreceptor by directly interacting with the core protein components of the circadian clock. (1354)