LIGHT-INDUCED DEGRADATION OF TIMELESS AND ENTRAINMENT OF THE DROSOPHILA CIRCADIAN CLOCK

Two genes, period (per) and timeless (tim), are required for productio n of circadian rhythms in Drosophila. The proteins encoded by these ge nes (PER and TIM) physically interact, and the timing of their associa tion and nuclear localization is believed to promote cycles of per and tim transcription through an autoregulatory feedback loop. Here it is shown that TIM protein may also couple this molecular pacemaker to th e environment, because TIM is rapidly degraded after exposure to light . TIM accumulated rhythmically in nuclei of eyes and in pacemaker cell s of the brain. The phase of these rhythms was differentially advanced or delayed by light pulses delivered at different times of day, corre sponding with phase shifts induced in the behavioral rhythms.