Originally published as Genetics Published Articles Ahead of Print on November 24, 2008.

Genetics, Vol. 181, 435-446, February 2009, Copyright © 2009
doi:10.1534/genetics.108.098145

A Systematic Screen for Transcriptional Regulators of the Yeast Cell Cycle

Department of Genetics and Center for Genome Sciences, Washington University School of Medicine, St. Louis, Missouri 63108

1 Corresponding author: Washington University School of Medicine, Campus Box 8510, 4444 Forest Park Ave., St. Louis, MO 63108.
E-mail: cohen{at}genetics.wustl.edu

Transcription factors play a key role in the regulation of cell cycle progression, yet many of the specific regulatory interactions that control cell cycle transcription are still unknown. To systematically identify new yeast cell cycle transcription factors, we used a quantitative flow cytometry assay to screen 268 transcription factor deletion strains for defects in cell cycle progression. Our results reveal that 20% of nonessential transcription factors have an impact on cell cycle progression, including several recently identified cyclin-dependent kinase (Cdk) targets, which have not previously been linked to cell cycle transcription. This expanded catalog of cell-cycle-associated transcription factors will be a valuable resource for decoding the transcriptional regulatory interactions that govern progression through the cell cycle. We conducted follow-up studies on Sfg1, a transcription factor with no previously known role in cell cycle progression. Deletion of Sfg1 retards cells in G1, and overexpression of Sfg1 delays cells in the G2/M phase. We find that Sfg1 represses early G1, Swi5/Ace2-regulated genes involved in mother–daughter cell separation. We also show that Sfg1, a known in vitro cyclin-dependent kinase target, is phosphorylated in vivo on conserved Cdk phosphorylation sites and that phosphorylation of Sfg1 is necessary for its role in promoting cell cycle progression. Overall, our work increases the number of transcription factors associated with cell cycle progression, strongly indicates that there are many more unexplored connections between the Cdk–cyclin oscillator and cell cycle transcription, and suggests a new mechanism for the regulation of cell separation during the M/G1 phase transition.


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