Coupling Phosphate Homeostasis to Cell Cycle-Specific Transcription: Mitotic Activation of Saccharomyces cerevisiae PHO5 by Mcm1 and Forkhead Proteins

Abstract

Cells devote considerable resources to nutrient homeostasis, involving nutrient surveillance, acquisition, and storage at physiologically relevant concentrations. Many Saccharomyces cerevisiae transcripts coding for proteins with nutrient uptake functions exhibit peak periodic accumulation during M phase, indicating that an important aspect of nutrient homeostasis involves transcriptional regulation. Inorganic phosphate is a central macronutrient that we have previously shown oscillates inversely with mitotic activation of PHO5. The mechanism of this periodic cell cycle expression remains unknown. To date, only two sequence-specific activators, Pho4 and Pho2, were known to induce PHO5 transcription. We provide here evidence that Mcm1, a MADS-box protein, is essential for PHO5 mitotic activation. In addition, we found that cells simultaneously lacking the forkhead proteins, Fkh1 and Fkh2, exhibited a 2.5-fold decrease in PHO5 expression. The Mcm1-Fkh2 complex, first shown to transactivate genes within the CLB2 cluster that drive G 2 /M progression, also associated directly at the PHO5 promoter in a cell cycle-dependent manner in chromatin immunoprecipitation assays. Sds3, a component specific to the Rpd3L histone deacetylase complex, was also recruited to PHO5 in G 1 . These findings provide (i) further mechanistic insight into PHO5 mitotic activation, (ii) demonstrate that Mcm1-Fkh2 can function combinatorially with other activators to yield late M/G 1 induction, and (iii) couple the mitotic cell cycle progression machinery to cellular phosphate homeostasis.Cellular growth and division are controlled by the temporal execution of programmed events that drive cell cycle progression. Several mechanisms that regulate the cell division cycle of S. cerevisiae are orchestrated by the cyclin-dependent kinase (CDK) Cdc28. While in large part this regulation occurs at the posttranscriptional level through targeted protein degradation (65), an important aspect of cell cycle regulation is also mediated at the level of transcription. More than 13% of S. cerevisiae genes are expressed in a cell cycle stage-specific fashion predominantly, yet not exclusively, via the action of one of three distinct classes of sequence-specific DNA-binding factors (16,68,81). These include SBF/MBF, Ace2/Swi5, and Mcm1, which respectively regulate G 1 /S-, M-, and M/G 1 -dependent transcription (81). These stage-specific roles are an approximation since some overlap occurs, most notably for Mcm1, which exhibits important functions throughout the cell cycle (23, 53).Budding yeast Mcm1, along with Agamous and Deficiens in plants and mammalian serum response factor, is a founding member of a family of proteins containing the highly conserved 56-amino-acid MADS box (58,63,80,95). Mcm1 is an essential gene product with diverse cellular roles in minichromosome maintenance, from which its name is derived, as well as cell cycle control, cell type determination, mating, arginine metabolism, and stress tolerance (14,54,78). Eighty amino acids near the N t...

The RSC chromatin remodeling complex has a crucial role in the complete remodeler set for yeast PHO5 promoter opening

“…To compare both strains under the same cell cycle arrest conditions, we used PHO5 induction conditions previously described by Pondugula et al (56). Here, the gene CDC20 encoding an essential activator of the anaphase-promoting-complex/cyclosome (APC/C) is placed under control of the GAL1 promoter ( P GAL1 :: CDC20 ).…”

MethylViewer: computational analysis and editing for bisulfite sequencing and methyltransferase accessibility protocol for individual templates (MAPit) projects

“…The settings for Base calling cutoff and Word size, were 200 and 15, respectively. ( C ) Overall methylation frequencies at each CCD site are indicated below the map showing placement of: positioned nucleosomes (ellipses labeled N−1, N−2 and N−3; Almer and Hörz, (82); upstream activating sequences at which Pho4 binds [red-filled circles labeled UASp1 and UASp2 as mapped by Vogel and Hinnen (83)]; the compound Mcm1-Fkh site [cyan-filled rectangle labeled UASm as described in Pondugula et al (81)]; and TATA box (white-filled square); major TSS (bent arrow). According to the convention used in budding yeast, base pair coordinates are indicated relative to the first nucleotide of the ATG translational initiation start codon.…”

Ectomycorrhizal fungi: the symbiotic route to the root for phosphorus in forest soils

“…Numerous studies have demonstrated an inverse relationship between acid phosphomonoesterase production by mycelia in axenic culture and P i availability (eg Doumas et al 1986;Mousain and Salsac 1986;Antibus et al 1986;Kroehler et al 1988;Tibbett et al 1998b) and for ECM roots (Bartlett and Lewis 1973;Alexander and Hardy 1981), indicating that synthesis of the enzyme is repressed when P i is readily available (Tibbett et al 1998b). In S. cerevisiae, cytoplasmic P i concentration regulates transcription of genes for secreted phosphatase (Lenburg and O'Shea 1996;Wykoff et al 2007;Pondugula et al 2009) and it seems reasonable to suggest that a similar pattern of regulation will also apply in ECM fungi.…”