Project description:H2A.Z acetylation has been suggested to regulate genes but effects on gene expression globally have not been reported. We find that the H2A.Z acetylation sites are required for normal growth in the presence of caffeine and therefore examined the gene expression response to caffeine when H2A.Z can’t be acetylated. Surprisingly we found little or no change in gene induction but a marked failure to remove H2A.Z from activated promoters. Caffeine causes a proteasome-dependent degradation of H2A.Z that is impaired in the absence of the H2A.Z acetylation sites. The proteasomal regulator Blm10 that has previously been implicated in acetylation-dependent histone degradation is required for H2A.Z degradation, revealing a novel role for acetylation in regulating H2A.Z protein levels. When H2A.Z levels are raised, either through loss of the acetylation sites or overexpression of the protein, a shared set of genes aberrantly retains H2A.Z at their 5’ ends during the caffeine response. As a result, expression of these genes fails to return to normal levels. H2A.Z is therefore subject to post-translational proteasomal regulation that controls protein levels, and the fine-tuning of gene expression during a stress response requires the normal function of this pathway. This regulation of H2A.Z degradation by acetylation is a previously unrecognised aspect of gene regulation.
Project description:Among the collection of chromatin modifications that influence its function and structure, the substitution of canonical histones by the so-called histone variants is one of the most prominent actions. Since crucial meiotic transactions are modulated by chromatin, here we investigate the functional contribution of the H2A.Z histone variant during both unperturbed meiosis and upon challenging conditions where the meiotic recombination checkpoint is triggered in budding yeast by the absence of the synaptonemal complex component Zip1. We have found that H2A.Z localizes to meiotic chromosomes in an SWR1-dependent manner. Although meiotic recombination is not substantially altered, the htz1 mutant (lacking H2A.Z) shows slower meiotic progression, impaired sporulation and reduced spore viability. These phenotypes are likely accounted for by the misregulation of meiotic gene expression landscape observed in htz1. In the zip1 mutant, the absence of H2A.Z results in a tighter meiotic arrest imposed by the meiotic recombination checkpoint. We have found that Mec1-dependent Hop1-T318 phosphorylation and the ensuing Mek1 activation are not significantly altered in zip1 htz1; however, downstream checkpoint targets, such as the meiosis I-promoting factors Ndt80, Cdc5 and Clb1, are drastically down-regulated. The study of the checkpoint response in zip1 htz1 has also allowed us to reveal the existence of an additional function of the Swe1 kinase, independent of CDK inhibitory phosphorylation, which is relevant to restrain meiotic cell cycle progression. In summary, our study shows that the H2A.Z histone variant impacts various aspects of meiotic development adding further insight into the relevance of chromatin dynamics for accurate gametogenesis.
Project description:Chromatin structure and function is regulated by reader proteins recognizing histone modifications and/or histone variants. We recently identified PWWP2A, which tightly binds to H2A.Z-containing nucleosomes and is involved in mitotic progression and cranial-facial development. Here, using in vitro assays we show that distinct domains of PWWP2A moreover mediate binding to free linker DNA as well as H3K36me3 nucleosomes. In vivo, PWWP2A strongly recognizes H2A.Z-containing regulatory regions and weakly H3K36me3-containing gene bodies. Additionally, PWWP2A bind to an MTA1-specific core NuRD (M1HR) complex solely consisting of MTA1, HDAC1 and RBBP4/7, excluding CHD and MBD proteins. Depletion of PWWP2A leads to an increase of acetylation levels on H3K27 as well as H2A.Z, presumably by impaired chromatin recruitment of M1HR. Thus, this study identifies PWWP2A as an ever more complex chromatin binding protein serving as adapter for M1HR to H2A.Z-containing chromatin, thereby promoting changes in histone acetylation levels and likely fine-tuning the transcriptional balance.
Project description:Quantitative MS analysis of acetylation in yeast using SILAC labeling and MaxQuant. Download Index of Raw files first. We used quantitative mass spectrometry to analyze acetylation dynamics and stoichiometry in Saccharomyces cerevisiae. We found that acetylation accumulated in growth-arrested cells in a manner that depended on acetyl-CoA generation in distinct subcellular compartments. We used stable isotope labeling with amino acids in cell culture to quantify differences in protein, acetylation, and phosphorylation abundance by MS. Proteins from whole cell lysates were digested to peptides and acetylated peptides enriched using a polyclonal anti-acetyllysine antibody. Peptide fractions were analyzed by reversed-phase liquid chromatography coupled to high resolution liquid chromatography‐tandem mass spectrometry (LC-MS/MS) and raw MS data were computationally processed using MaxQuant.
Project description:In the budding yeast Saccharomyces cerevisiae, transcription factors (TFs) regulate the periodic expression of many genes during the cell cycle, including gene products required for progression through cell-cycle events. Experimental evidence coupled with quantitative models suggest that a network of interconnected TFs is capable of regulating periodic genes over the cell cycle. Importantly, these dynamical models were built on transcriptomics data and assumed that TF protein levels and activity are directly correlated with mRNA abundance. To ask whether TF transcripts match protein expression levels as cells progress through the cell cycle, we applied a multiplexed targeted mass spectrometry approach (parallel reaction monitoring) on synchronized populations of cells. We found that protein expression of many TFs and cell-cycle regulators closely followed their respective mRNA transcript dynamics in cycling wild-type cells. Discordant mRNA/protein expression dynamics were also observed for a subset of cell-cycle TFs and for proteins targeted for degradation by E3 ubiquitin ligase complexes such as SCF (Skp1/Cul1/F-box) and APC/C (anaphase-promoting complex/cyclosome). We further profiled mutant cells lacking B-type cyclin/CDK activity (clb1-6), where oscillations in ubiquitin ligase activity, cyclin/CDKs, and cell-cycle progression are halted. We found that a number of proteins were no longer periodically degraded in clb1-6 mutants compared to wild type, highlighting the importance of post-transcriptional regulation. Finally, the TF complexes responsible for activating G1/S transcription (SBF and MBF) were more constitutively expressed at the protein level than their periodic mRNA expression levels in both wild-type and mutant cells. This comprehensive investigation of cell-cycle regulators reveals that multiple layers of regulation (transcription, protein stability, and proteasome targeting) affect protein expression dynamics during the cell cycle.
Project description:In this study, we characterize the protein uptake and degradation pathways of S. cerevisiae to better understand its impact on protein secretion titers. We do find that S. cerevisiae can consume significant (g/L) quantities of whole proteins. Characterizing the systems with metabolomics and transcriptomics, we identify metabolic and regulatory markers that are consistent with uptake of whole proteins by endocytosis, followed by intracellular degradation and catabolism of substituent amino acids. Uptake and degradation of recombinant protein products may be common in S. cerevisiae protein secretion systems, and the current data should help formulate strategies to mitigate product loss.