Project description:The budding yeast genome is marked by 250-350 origins of DNA replication. These origins are bound by the origin recognition complex (ORC) throughout the cell cycle. ORC has known DNA binding sequence preferences which, though necessary for binding, are not sufficient to fully specify a genomic locus as being bound by ORC, indicating that the cell must use additional chromosomal cues to specify ORC binding sites and origins of replication. Using high-throughput sequencing to precisely locate both ORC binding sites and nucleosome locations genome-wide, we find that a nucleosome depleted region (NDR) and precisely positioned nucleosomes are a ubiquitous feature of yeast replication origins. The ARS consensus sequence (ACS) and adjacent sequences are sufficient to maintain the nucleosome-free properties of the NDR. We use a temperature sensitive ORC1 mutant to demonstrate that ORC is required to maintain precisely positioned nucleosomes at origins of replication. These findings demonstrate the importance of local nucleosome positioning at replication origins, and that chromatin organization is an important determinant of origin selection.
Project description:The budding yeast genome is marked by 250-350 origins of DNA replication. These origins are bound by the origin recognition complex (ORC) throughout the cell cycle. ORC has known DNA binding sequence preferences which, though necessary for binding, are not sufficient to fully specify a genomic locus as being bound by ORC, indicating that the cell must use additional chromosomal cues to specify ORC binding sites and origins of replication. Using high-throughput sequencing to precisely locate both ORC binding sites and nucleosome locations genome-wide, we find that a nucleosome depleted region (NDR) and precisely positioned nucleosomes are a ubiquitous feature of yeast replication origins. The ARS consensus sequence (ACS) and adjacent sequences are sufficient to maintain the nucleosome-free properties of the NDR. We use a temperature sensitive ORC1 mutant to demonstrate that ORC is required to maintain precisely positioned nucleosomes at origins of replication. These findings demonstrate the importance of local nucleosome positioning at replication origins, and that chromatin organization is an important determinant of origin selection. Examination of nucleosome positioning in wild-type and orc1-161ts mutant S. cerevisiae at room temperature and heatshock temperatures. Examination of ORC binding locations by ChIP-seq. All reported coordinates are based on the SGD genome build released 12/16/2005.
Project description:We developed an artificial genome evolution system, which we termed ‘TAQing’, by introducing multiple genomic DNA double-strand breaks using a heat-activatable endonuclease in mitotic yeast. The heat-activated endonuclease, TaqI, induced random DSBs, which resulted in diverse types of chromosomal rearrangements including translocations. Array comparative genomic hybridization (aCGH) analysis was performed with cell-fused Saccharomyces cerevisiae strains induced genome evolution by TAQing system. Some of copy number variations (CNVs) induced by massive genome rearrangements were detected in the TAQed yeast strains.
Project description:We report the application of single-molecule-based sequencing technology for high-throughput profiling of histone modifications in yeast. By obtaining bases of sequence from chromatin immunoprecipitated DNA, we generated genome-wide chromatin-state maps of saccharomuces cerevisiae.We find that H3T11 phosphorylationlysine is widely distributed in gene promoter region and chromosome telomere region
Project description:Sumoylation is emerging as a post-translation modification important for chromosome duplication and stability. The origin recognition complex (ORC), which directs DNA replication initiation by loading the MCM replicative helicases onto origins, is sumoylated in both yeast and human cells. However, the biological consequences of ORC sumoylation are largely unclear. Here we report the effects of hyper- and hypo-sumoylation of yeast ORC using multiple approaches. We show that ORC hyper-sumoylation preferentially reduces the activity of a subset of early origins, while Orc2 hypo-sumoylation has an opposing effect. Mechanistically, ORC hyper-sumoylation leads to reduced MCM loading in vitro and diminished MCM chromatin association in vivo. The importance of an appropriate level of ORC sumoylation is suggested by the data that either hyper- or hypo-sumoylation of ORC results in genome instability and a dependence on other genome maintenance factors for cell fitness. Thus, yeast ORC sumoylation status needs to be fine-tuned to achieve optimal origin activity control and genome stability.
Project description:A network governing DNA integrity was identified in yeast by a global genetic analysis of synthetic fitness or lethality defect (SFL) interactions. Within this network, multiple functional modules or mini-pathways were defined according to their common patterns of global SFL interactions and available protein-protein interaction information. Modules or genes involved in DNA replication, DNA replication checkpoint signaling, and oxidative stress response were identified as the major guardians against lethal spontaneous DNA damage, efficient repair of which requires the functions of the DNA damage checkpoint signaling and multiple DNA repair pathways. This genome-wide genetic interaction network also revealed potential roles of a number of genes and modules in mitotic DNA replication and maintenance of genomic stability. These include DIA2, NPT1, HST3, HST4, and the CSM1/LRS4 module (CSM1m). Likewise, the CTF18 module (CTF18m), previously implicated in sister chromatid cohesion, was found to participate in the DNA replication checkpoint. Keywords: dose response
Project description:To characterize the ecological interactions among S. cerevisiae strains coming from the same geographical area, we examined the fitness of two natural isolates from San Giovese grapes, alone or in competition, in synthetic wine must (SWM). We performed genome-wide analyses in order to identify the genes involved in yeast competition and cooperation.
Project description:To determine the genomic location of a gene that permits xylose utilization we conducted bulk segregant analysis (BSA) using Affymetrix yeast tiling arrays. BSA works by taking advantage of DNA sequence polymorphisms between different strains and the fact that it is relatively easy to pool large numbers of meiotic spore products (segregants) in yeast. Pooling segregants based on their phenotype allows the region of the genome responsible for the phenotype to be detected. This is because DNA polymorphisms in regions unlinked to the locus causing the phenotype will segregate randomly and be “evened” out, while around the genomic region of interest, sequences or polymorphisms responsible for the trait will be present in all positive segregants, and absent in all negative segregants. In our case, a Simi White wine strain (S. cerevisiae) carrying the locus responsible for xylose utilization was crossed to a laboratory strain of Saccharomyces cerevisiae; this strain was estimated to carry DNA polymorphisms relative to the laboratory strain at a level of approximately .5%. Spores from the Simi White / S288c diploid were screened for the xylose utilization phenotype and 39 positive spores were combined into one pool and 39 negative spores into another pool, and genomic DNA (gDNA) was isolated from each pool. We then hybridized the positive and negative gDNA pools to tiling microarrays that were based on the S288c reference genome with the expectation that regions of the genome derived from Simi White will hybridize less robustly to the array because of the DNA polymorphisms between Simi White and S288c. Log2 ratios of probe intensities were calculated (negative/positive), and a peak appeared in the chromosome XV right subtelomeric region that corresponds to less robust hybridization to the microarray of the positive pool gDNA coming from this region of the genome
Project description:Mapping of nucleosomes, the basic DNA packaging unit in eukaryotes, is fundamental for understanding genome regulation as nucleosomes modulate DNA access by their positioning along the genome. A cell population nucleosome map requires two observables: nucleosome positions along the DNA (“Where?”) and nucleosome occupancies across the population (“In how many cells?”). All available genome-wide nucleosome mapping techniques are yield methods as they score either nucleosomal (e.g., MNase-seq, chemical cleavage-seq) or non-nucleosomal (e.g., ATAC-seq) DNA but lose track of the total DNA population for each genomic region. Therefore, they only provide nucleosome positions and maybe compare relative occupancies between positions but cannot measure absolute nucleosome occupancy, which is the fraction of all DNA molecules occupied at a given position and time by a nucleosome. Here, we established two orthogonal and thereby crossvalidating approaches to measure absolute nucleosome occupancy across the Saccharomyces cerevisiae genome via restriction enzymes and DNA methyltransferases. The resulting high-resolution (9 bp) map shows uniform absolute occupancies. Most nucleosome positions are occupied in most cells: 97% of all nucleosomes called by chemical cleavage-seq have a mean absolute occupancy of 90 ± 6% (± SD). Depending on nucleosome position calling procedures, there are 57-60,000 nucleosomes per yeast cell. The few low absolute occupancy nucleosomes do not correlate with highly transcribed gene bodies, but with increased presence of the nucleosome-evicting RSC chromatin remodeling complex there and are enriched upstream of highly transcribed or regulated genes. Our work provides a quantitative method and reference frame in absolute terms for future chromatin studies.