ISOLATION OF TIMELESS BY PER PROTEIN-INTERACTION - DEFECTIVE INTERACTION BETWEEN TIMELESS PROTEIN AND LONG-PERIOD MUTANT PER(L)

The period (per) gene likely encodes a component of the Drosophila cir cadian clock. Circadian oscillations in the abundance of per messenger RNA and per protein (PER) are thought to arise from negative feedback control of per gene transcription by PER. A recently identified secon d clock locus, timeless (tim), apparently regulates entry of PER into the nucleus. Reported here are the cloning of complementary DNAs deriv ed from the tim gene in a two-hybrid screen for PER-interacting protei ns and the demonstration of a physical interaction between the tim pro tein (TIM) and PER in vitro. A restricted segment of TIM binds directl y to a part of the PER dimerization domain PAS. PER(L), a mutation tha t causes a temperature-sensitive lengthening of circadian period and a temperature-sensitive delay in PER nuclear entry, exhibits a temperat ure-sensitive defect in binding to TIM. These results suggest that the interaction between TIM and PER determines the timing of PER nuclear entry and therefore the duration of part of the circadian cycle.