[Molecular mechanism of biological clock: for chronobiological approach to stress].

Recent progress in molecular chronobiology revealed that the clock genes control intracellular feedback loops. CLOCK protein and BMAL1 protein, first discovered as components of the circadian clock in mammals, are known to function as transcriptional activators in the circadian feedback loop of drosophila. PERIOD and TIMELESS proteins work as inhibitors for these activators in drosophila and possibly in mammals. The clock genes described above are also expressed in peripheral tissues with circadian rhythmicity. Cultured rat-1 fibroblast shows circadian expression of clock genes after serum shock or forskolin stimulation. These results indicate that the clock genes function not only as components of the endogenous clock, but also as a coordinator of the circadian activity of peripheral tissues. It will be important to study stress from the aspect of circadian rhythm.