Arabidopsis 6%: Drosophila between 1% and 5%: mouse 5% to 10% %
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||p.422 left column bottom paragraph:"The extent of circadian cycling observed in the transcriptome was a surprise to many researchers. In Arabidopsis 6%, in Drosophila between 1% and 5%, and in mouse 5% to 10% of transcripts were identified as circadian (primary sources 24, 35, 97 reviewed in primary source 23). In addition, enhancer trapping in Arabidopsis found that one-third of the promoters examined showed circadian rhythmicity, confirming the impact of the clock on transcriptional regulation (ref 82). This large number of cycling transcripts may be one explanation for why forward genetic screens, which were very successful at identifying core-clock components, were relatively poor at identifying components of the output pathways given that compensation by other output signals could mask the loss of any individual component. A second commonality between the Arabidopsis, Drosophila, and mouse [specifically, the suprachiasmatic nucleus (SCN)] arrays was the observation of a bimodal distribution of the cycling transcripts. That is, most circadian expressed genes showed peak expression either immediately before dawn or dusk, reflecting the importance of anticipating daily light transitions."