Role of molecular oscillations in generating behavioral rhythms in Drosophila

Circadian oscillations of clock gene products are thought to provide time-o f-day signals that drive overt rhythms. In Drosophila, RNA and protein leve ls of the period and timeless genes oscillate and the proteins autoregulate their transcription. To test the relevance of these oscillations, we expre ssed period and timeless under control of constitutively active promoters. Constitutive expression of either RNA supported protein cycling and behavio ral rhythms in the respective null mutant, although constitutive timeless w as less effective than constitutive period. Constitutive expression of both genes restored behavioral rhythms that showed deficits in photic resetting and drove cyclic expression of the clock-controlled RNA, vrille. Overexpre ssion of either period or timeless, but especially timeless, attenuated beh avioral rhythmicity and protein cycling in lateral neurons. We propose that the two proteins must cycle to drive rhythmic expression of downstream gen es.