Repression of essential cell cycle genes increases cellular fitness

Abstract

A network of transcription factors (TFs) coordinates transcription with cell cycle events in eukaryotes. Most TFs in the network are phosphorylated by cyclin-dependent kinase (CDK), which limits their activities during the cell cycle. Here, we investigate the physiological consequences of disrupting CDK regulation of the paralogous repressors Yhp1 and Yox1 in yeast. Blocking Yhp1/Yox1 phosphorylation increases their levels and decreases expression of essential cell cycle regulatory genes which, unexpectedly, increases cellular fitness in optimal growth conditions. Using synthetic genetic interaction screens, we find that Yhp1/Yox1 mutations improve the fitness of mutants with mitotic defects, including condensin mutants. Blocking Yhp1/Yox1 phosphorylation simultaneously accelerates the G1/S transition and delays mitotic exit, without decreasing proliferation rate. This mitotic delay partially reverses the chromosome segregation defect of condensin mutants, potentially explaining their increased fitness when combined with Yhp1/Yox1 phosphomutants. These findings reveal how altering expression of cell cycle genes leads to a redistribution of cell cycle timing and confers a fitness advantage to cells.

Calcineurin promotes adaptation to chronic stress through two distinct mechanisms

“…Consistent with previous studies, deletion of the CN-regulatory subunit CNB1 had no detectable effect on the proliferation of cells growing on agar plates containing 0.2 M CaCl 2 (Figure 1A) (Nakamura et al ., 1996; Withee et al ., 1997, 1998; Mulet et al ., 2006; Ferreira et al ., 2012; Xu et al ., 2019). Since growth on plates does not always reveal modest differences in proliferation rate, we also examined the competitive growth of CN mutant strains grown in co-culture with a wild-type strain in a more sensitive assay (Conti et al ., 2022). Briefly, one strain expressing GFP is co-cultured with a strain expressing a mutated, non-fluorescent GFP(Y66F) (Supplemental Figure S1A).…”

“…Where indicated, media also contained 0.2 M CaCl 2 , 0.4 M KCl, and/or 250 μM reduced L-glutathione (Sigma), 250 μM DL-homocysteine (Sigma), or 5 mM ascorbic acid (Sigma). Marker strains for competitive fitness assays (GFP+ and GFP-) were constructed as previously described (Conti et al ., 2022). Any additional genetic manipulations in competition strains (i.e., gene deletions) were introduced by genetic cross between the marker strains and strains containing the desired mutation.…”

Revealing the Mechanism of Aroma Production Driven by High Salt Stress in Trichomonascus ciferrii WLW

“…Their significant upregulation during the pre-salt stress period (Days 2-4) (Figure 5A,B) might contribute to the high salt tolerance of T. ciferrii WLW. YOX1/YHP1 are co-repressors of DNA transcription, and when DNA replication is stressed, high YOX1 expression (Figure 5C) blocks cell cycle progression until it is able to overcome replication defects [55], thereby increasing cellular resilience to environmental stress [56], which might be an important reason for the high salt tolerance of T. ciferrii WLW. However, the downregulation of CAT8 accelerates cell growth and glucose consumption, and alters the type of energy metabolism in yeast cells, in which many genes In terms of TFs, which are important for regulating stress response [52], we analyzed the TF data obtained from DEGs under salt stress conditions based on the JASPAR database (http://jaspar.genereg.net/, accessed on 12 October 2019).…”

Phosphosite Scanning reveals a complex phosphorylation code underlying CDK-dependent activation of Hcm1

“…All genomic mutations were confirmed by sequencing. GAL1p-HCM1 was introduced into strains for pairwise competition assays by genetic cross with previously characterized strains expressing WT or non-fluorescent GFP 43 .…”