# HHMI and Dept. of Biology, Brandeis University, Waltham MA, USA, % Dept.de Biologie Moléculaire, Institut Pasteur, Paris, France,
Circadian rhythms of locomotor activity and eclosion in Drosophila depend upon the reciprocal autoregulation of the PERIOD (PER) and TIMELESS (TIM) proteins on the transcription of their own genes. The circadianly controlled entry of PER and TIM proteins in the nucleus of pacemaker cells triggers the decrease of per and tim mRNAs levels. These features suggest that PER and TIM proteins could also control the circadian expression of clock output genes. We report the isolation of CRG-1, a new circadianly regulated gene. Like per and tim transcripts, the CRG-1 transcript levels show 24 hr. oscillations in light:dark conditions in wild type flies, with a maximal abundance at the beginning of the night. These oscillations persist in complete darkness and depend on PER and TIM proteins. The putative CRG-1 translation products show some sequence similarity with the DNA-binding domain of the HNF-3/fork head family of transcription factors. In situ hybridization analysis reveals that CRG-1 expression in the adult head is restricted to the subsets of per expressing cells in the eyes, optic lobes and central brain, suggesting possible interactions between CRG-1 and the known clock components.