REGULATION OF THE DROSOPHILA PROTEIN TIMELESS SUGGESTS A MECHANISM FOR RESETTING THE CIRCADIAN CLOCK BY LIGHT

Circadian behavioral rhythms in Drosophila depend on the appropriate r egulation of at least two genes, period (per) and timeless (tim). Prev ious studies demonstrated that levels of PER and TIM RNA cycle with th e same phase and that the PER and TIM proteins interact directly. Here we show the cyclic expression of TIM protein in adult heads and repor t that it lags behind peak levels of TIM RNA by several hours. We also show that nuclear expression of TIM depends upon the expression of PE R protein. Finally, we report that the expression of TIM, but not PER, is rapidly reduced by light, suggesting that TIM mediates light-induc ed resetting of the circadian clock. Since both PER and TIM RNA are un affected by light treatment, the effects of light on TIM appear to be posttranscriptional.