ABSTRACT: RNA polymerase III (pol III) synthesizes short non-coding RNAs, many of which, including tRNAs, Rpph1 RNA, Rn5s rRNA, and Rmrp RNA, are essential for translation. Accordingly, pol III activity is tightly regulated with cell growth and proliferation by factors such as MYC, RB1, TRP53, and MAF1. MAF1 is a repressor of pol III transcription whose activity is controlled by phosphorylation; in particular, it is inactivated through phosphorylation by mTORC1 kinase, a sensor of nutrient availability. Pol III regulation is thus sensitive to environmental cues, yet a diurnal profile of pol III transcription activity is so far lacking. Here we document pol III occupancy of its target genes in mouse liver during the diurnal cycle and show that pol III occupancy rises before the onset of the night, stays high during the night, when mice normally ingest food and when translation is increased, and decreases in daytime. By comparing diurnal pol III occupancy in wild-type mice, arrhythmic mice owing to inactivation of the Arntl gene, mice fed at regular intervals during both night and day, and mice lacking the Maf1 gene, we show that whereas higher pol III occupancy during the night reflects a MAF1-dependent response to feeding, the rise of pol III occupancy before the onset of the night reflects a circadian clock-dependent response. Thus, pol III transcription during the diurnal cycle is regulated both in response to nutrients and by the circadian clock, which allows anticipatory pol III transcription.
