Circadian clocks in the bodies of humans ensure that functions such as the sleep/wake cycle, body temperature, hormonal secretion, cardiovascular function, respiration and metabolism are timed correctly. There is an exceptionally high degree of conservation between the circadian clocks of mammals and insects and much of our current understanding of clock function in humans is based on studies of the genes and the molecular circuits of the clock in model organisms such as Drosophila. Transcriptional feedback circuits responsible for the autonomous pacemaker function of the Drosophila clock have been identified in detail, but much less is known about the pathways connecting these circuits to overt rhythms in physiology and behavior. This proposal is designed to test the hypothesis that the CLK/CYC transcription factor of the Drosophila clock circuits has direct transcriptional targets in the Drosophila brain that generate behavioral rhythms. Specific Aims: (1) Transcriptional targets specific to the circadian transcription factor CLK/CYC will be identified with the use of a set of transgenic flies that allow expression of each of these transcription factors to be induced individually in clock-bearing cells. (2) Direct transcriptional targets for CLK/CYC will be identified by luciferase reporter assays and chromatin immunoprecipitation experiments performed in Drosophila S2 cells. (3) Locomotor and eclosion behavior phenotypes associated with primary transcriptional clock output in the brain will be determined with the use of transgenic flies. Significance: The insight provided by the proposed studies into the internal time keeping mechanisms of animals is not only relevant to diseases associated with disruptions of these mechanisms (sleep disorders, cancer, diabetes), but also more generally to diagnostic and treatment procedures involving bodily functions that show regular daily variations.