Project description:It is widely believed that reorganization of nucleosomes result in availability of transcription factor (TF) binding sites for eukaryotic gene regulation. Recent findings also show TFs induced during physiological perturbations can alter nucleosome occupancy to facilitate DNA binding. Although, these suggest a close relationship between TF binding and nucleosomes, the nature of this interaction, or to what extent it influences transcription is not clear. Moreover, since physiological perturbations induced multiple TFs, relatively direct effect of any TF on nucleosome occupancy remains poorly addressed. With these in mind, we used a single TF to induce physiological changes and following characterization of the two states (before and after induction of the TF) we determined: (a) genome wide binding sites of the TF, (b) promoter nucleosome occupancy and (c) transcriptome profiles, independently in both conditions. We find only ~20% of TF binding results from nucleosome repositioning - interestingly, almost all corresponding genes were transcriptionally altered. Whereas, when TF-occupancy was independent of nucleosome repositioning only a small fraction of corresponding genes were expressed/repressed. These observations suggest a model where TF occupancy leads to transcriptional change only when coupled with nucleosome repositioning in close proximity. This, to our knowledge, for the first time also helps explain why genome wide TF occupancy (e.g., from ChIP-sequencing) typically overlaps with only a small fraction of genes that change expression. The nature of interaction between TF binding and nucleosomes and what extent it influences transcription
Project description:We describe the genome-wide nucleosome profiles of four related yeast species. All species display the same global organization features first described in S. cerevisiae: a stereotypical nucleosome organization along genes, and the classification of promoters into these which contain or lack a pronounced Nucleosome Depleted region (NDR), with the latter displaying a more dynamic pattern of gene expression. This global similarity, however, does not reflect a static evolutionary pattern, as nucleosome positioning at specific genes diverged rapidly leaving practically no similarity between S. cerevisiae and C. glabrata orthologs (~50 Myr). We show that this rapid divergence in nucleosome positioning contrasts a conserved pattern of gene expression, consistent with the idea that divergence of nucleosome patterns has a limited effect on gene expression as many different configurations can support the same regulatory outcome. Nucleosomes from 4 different yeast species were isolated and sequenced using the Illumina GAII platform. Replicates were performed for 3 of the species
Project description:We describe the genome-wide nucleosome profiles of four related yeast species. All species display the same global organization features first described in S. cerevisiae: a stereotypical nucleosome organization along genes, and the classification of promoters into these which contain or lack a pronounced Nucleosome Depleted region (NDR), with the latter displaying a more dynamic pattern of gene expression. This global similarity, however, does not reflect a static evolutionary pattern, as nucleosome positioning at specific genes diverged rapidly leaving practically no similarity between S. cerevisiae and C. glabrata orthologs (~50 Myr). We show that this rapid divergence in nucleosome positioning contrasts a conserved pattern of gene expression, consistent with the idea that divergence of nucleosome patterns has a limited effect on gene expression as many different configurations can support the same regulatory outcome.
Project description:It is widely believed that reorganization of nucleosomes result in availability of transcription factor (TF) binding sites for eukaryotic gene regulation. Recent findings also show TFs induced during physiological perturbations can alter nucleosome occupancy to facilitate DNA binding. Although, these suggest a close relationship between TF binding and nucleosomes, the nature of this interaction, or to what extent it influences transcription is not clear. Moreover, since physiological perturbations induced multiple TFs, relatively direct effect of any TF on nucleosome occupancy remains poorly addressed. With these in mind, we used a single TF to induce physiological changes and following characterization of the two states (before and after induction of the TF) we determined: (a) genome wide binding sites of the TF, (b) promoter nucleosome occupancy and (c) transcriptome profiles, independently in both conditions. We find only ~20% of TF binding results from nucleosome repositioning - interestingly, almost all corresponding genes were transcriptionally altered. Whereas, when TF-occupancy was independent of nucleosome repositioning only a small fraction of corresponding genes were expressed/repressed. These observations suggest a model where TF occupancy leads to transcriptional change only when coupled with nucleosome repositioning in close proximity. This, to our knowledge, for the first time also helps explain why genome wide TF occupancy (e.g., from ChIP-sequencing) typically overlaps with only a small fraction of genes that change expression.
Project description:The effect of overexpression of the gene ADH2 on metabolic and biological activity in Saccharomyces bayanus V5 during alcoholic fermentation has been evaluated. This gene is known to encode alcohol dehydrogenase II (ADH II). During the biological aging of sherry wines, where yeasts have to grow on ethanol owing to the absence of glucose, this isoenzyme plays a prominent role by converting the ethanol into acetaldehyde and producing NADH in the process. Overexpression of the gene ADH2 during alcoholic fermentation has no effect on the proteomic profile or the net production of some metabolites associated with glycolysis and alcoholic fermentation such as ethanol, acetaldehyde, and glycerol. However, it affects indirectly glucose and ammonium uptakes, cell growth, and intracellular redox potential, which lead to an altered metabolome. The increased contents in acetoin, acetic acid, and L-proline present in the fermentation medium under these conditions can be ascribed to detoxification by removal of excess acetaldehyde and the need to restore and maintain the intracellular redox potential balance.
Project description:Nucleosome positions were determined for purified S. cerevisiae quiescent cells and compared to logarithmically growing cells. By analyzing nucleosome positions and MNase digestion patterns for two separate matched digestion amounts (~80% and ~50% mononucleosomes) we show that global nucleosome stabilization and repositioning occurs at transcription start sites. This repositioning indicates a repressive chromatin architecture that reflects global transcriptional shutoff in quiescent yeast.
Project description:We identify the cis and trans determinants of nucleosome positioning using a functional evolutionary approach involving S. cerevisiae strains containing large genomic regions from other yeast species. In a foreign species, nucleosome depletion at promoters is maintained over poly(dA:dT) tracts, whereas internucleosome spacing and all other aspects of nucleosome positioning tested are not. Interestingly, the locations of the +1 nucleosome and RNA start sites shift in concert. Strikingly, in a foreign species, nucleosome-depleted regions occur fortuitously in coding regions, and they often act as promoters that are associated with a positioned nucleosome array linked to the length of the transcription unit. nucleosome mapping for 3 strains bearing yeast artificial chromosomes from Kluyveromyces lactis and 2 strains with Debaryomyces hansenii artificial chromosomes in Saccharomyces cerevisiae