We study the molecular bases of circadian timekeeping mechanism in mammals. We intend to understand the mechanism of light perception by specialized light sensitive ganglion cells of the retina which photo-entrain the master circadian oscillator resident in the hypothalamic SCN. We also want to understand the regulatory mechanisms which maintain a near 24 hours molecular rhythm in core oscillator components, and generate rhythms in gene function that ultimately produce several overt rhythms in physiology and behavior.