CIRCADIAN OSCILLATION OF 64-KDA POLYPEPTIDE IN THE RAT SUPRACHIASMATIC NUCLEUS

In cell suspensions of suprachiasmatic nucleus harvested every 3 hr fr om rats kept under 12 hr: 12 hr light-dark cycle and constant darkness , we have detected a Mr 64-kDa protein whose synthesis exhibits two di stinct daily peaks in SDS-PAGE. Analysis of densitometer tracings reve aled that the synthesis of other proteins was independent of the time of day or not reproducible. Maximum synthesis of the 64-kDa polypeptid e occurred at around CT6 and CT21, which are almost coincident with th e phase advance regions of circadian activity rhythm induced by anisom ycin and light pulses [15], respectively. These results suggest that t he 64-kDa protein in SDS-PAGE may be a part of the circadian clock mec hanism.