ABSTRACT
Drosophila have been the subject of circadian clock research for several decades. Several pieces of behavioral evidence indicate that per is intimately associated with the Drosophila circadian pacemaker. The per feedback loop is not only operating in cells that mediate locomotor activity rhythms, but also in other head and non-ovarian body cells. The mechanisms underlying circadian feedback regulation are being uncovered by identifying sequences and factors that control per transcription. Molecular analysis of per provided a basic clock mechanism, but it did not elucidate the mechanisms that synchronize the clock to light. As far as other components of the circadian system are concerned, the Drosophila system, sadly enough, does not contribute much. Although a couple of per downstream genes have been cloned, their function and their location within the output pathway are not known.
