A Systematic Screen for Transcriptional Regulators of the Yeast Cell Cycle

Abstract

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 G 1 , and overexpression of Sfg1 delays cells in the G 2 /M phase. We find that Sfg1 represses early G 1 , 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/G 1 phase transition.

Functional Genomics Analysis of theSaccharomyces cerevisiaeIron Responsive Transcription Factor Aft1 Reveals Iron-Independent Functions

“…Genome-wide genetic screens identify diverse cellular roles for Aft1: In an effort to further define the cellular functions of Aft1, SGA methodology was used to perform complementary genome-wide SL and SDL screens (Tables 2 and Tables 3). As expected, the genetic interaction map identified genes encoding proteins implicated in processes previously linked to Aft1 including iron regulation (reviewed in Rutherford and Bird 2004), chromosome stability (Measday et al 2005), cellcycle progression (Philpott et al 1998;Jorgensen et al 2002;White et al 2009), and DNA damage repair (Lee et al 2005;Kimura et al 2007). Further, the AFT1 genetic interaction map also predicts possible functional roles for Aft1 in cell-wall assembly, protein transport, and the mitochondria.…”

“…Systematic screens have determined that aft1D mutant cells are significantly larger than wild-type cells ( Jorgensen et al 2002) and are delayed in G1 (White et al 2009). Further, overexpression of AFT1 or aft1-1 up results in G1 arrest due to the inhibition of translation of G 1 cyclins by an undetermined mechanism (Casas et al 1997;Philpott et al 1998).…”

Neural development is dependent on the function of specificity protein 2 in cell cycle progression

“…In this context, the mitotic entry network involves upregulation of the cyclin B1-Cdk1 complex and its activation through post-transcriptional modifications (Fung and Poon, 2005;White et al, 2009;Lindqvist et al, 2009;Bollen et al, 2009). Notably, many kinases and phosphatases that form the mitotic entry network are also required for progression through M (Pomerening et al, 2008;Lindqvist et al, 2009;Bollen et al, 2009), for example by coupling timely G2-M transition to centrosome maturation for appropriate mitotic spindle orientation in neural progenitors (Gruber et al, 2011).…”

SIN3 is critical for stress resistance and modulates adult lifespan

“…Although not essential for yeast viability in normal conditions, ySin3 was shown to be important for accurate timing of Swi4/Swi6-regulated gene transcription during G1 and for activation of S phase in daughter cells [27]. Additionally, S. cerevisiae SIN3 was found to be important for cell cycle progression as null mutants of an asynchronous population accumulated in G2 phase relative to wild type cells [28]. …”