A novel protein interacts with a clock-related protein, rPer1

Mammalian Per proteins are thought to be important in the mechanism of circadian rhythm. We identified a novel protein PIPS (Per1 interacting protein of the suprachiasmatic nucleus) with the yeast two-hybrid system using PAS domain of rat Per1 (rPer1) as a bait. PIPS is about a 180-kDa protein and expressed mainly in the brain, especially in the hypothalamus including the suprachiasmatic nuclei (SCN). PIPS interacts with mouse Per1 (mPer1) in vitro and in cultured cells transfected with both molecules. Furthermore, it was found that mPer1 translocated PIPS into the nuclei in the cultured cells. Thus, these findings suggest a possibility that PIPS is involved in the feedback loop or output mechanism of circadian rhythm through interacting with Per1 in the SCN.