ABSTRACT: Open chromatin provides access to a wide spectrum of DNA binding proteins for DNA metabolism processes such as transcription, repair, recombination, and replication. In this regard, open chromatin profiling has been widely used to identify the location of regulatory regions, including promoters, enhancers, insulators, silencers, replication origins, and recombination hotspots. Regulatory DNA elements are made accessible by nucleosome-depeleted states. Thus, nucleosome remodelling and modification should be intimately coupled with open chromatin formation and regulation. However, our knowledge of nucleosome regulation is largely limited to promoter regions, which comprise only a subset of all regulatory loci in the genome. In order to examine nucleosome patterns in open chromatin regions, we performed micrococcal nuclease (MNase) sequencing for a laboratory strain of yeast. Nucleosome occupancy profiled by Micrococcal nuclease (MNase) digestion
Project description:Nucleosome structure directly influences gene transcription. However, the function of each histone residue remains largely unknown. Here we profiled gene expression changes upon the mutation of individual residues of histone H3 and H4. Histone residues grouped by expression change similarity displayed overall structural relevance. This regulatory functional map of the core histones led to novel findings. First, the residues specific to each histone family tend to be more influential than those commonly found among different histones. Second, unlike histone acetylations, H3K4 trimethylation does not appear to be prerequisite for gene activation. Third, H3Q5 has been newly identified for its putative interactions with many chromatin regulators for transcription control. Lastly, the nucleosome lateral surface seems to play a key role through interactions with the surrounding DNA. Remarkably, we discovered a novel role for H3K56 in chromatin dynamics. The deletion of this residue, but not the alteration of acetylation states, caused a genome-wide decrease in nucleosome mobility and stabilized nucleosome positioning near transcription start and end sites. Occupying the DNA entry/exit site, H3K56 is thought to modulate nucleosome sliding along DNA. Taken together, genomics approaches such as microarray and deep sequencing prove valuable for mapping the function of histone residues. Performing Mnase-seq for six histone mutants and two wild-types in Saccharomyces cerevisiae
Project description:To study the evolution of nucleosome positioning we mapped nucleosome positioning in two species of yeasts. Identified differences in nucleosome positioning were classified into cis-based changes or trans-bseed changes based on the pattern of nucleosomes in the hybrid. This analysis was performed for wild-type strains as well as for strains deleted of 5 chromatin regulatoirs allolwing us to examine their roles in determining nucleosome positioning. Illumina sequencing of mono-nucleosome fragments isolated by MNase digestion. Samples include pooled DNA fragments of S. cerevisiae and S. paradoxus or DNA fragments of the interspecific hybrid. Experiments were performed for WT strains as well as strains deleted of 5 chromatin regulators.
Project description:We and others have identified that MBD3/NuRD localizes at active promoters and enhancers, suggesting an active role of NuRD at open chromatin region. Because NuRD includes nucleosome remodelers, CHD3 and CHD4, we hypothesized that NuRD regulates nucleosome organization at open chromatin region. To test this idea, we performed micrococcal nuclease digestion followed by massively parallel sequencing (MNase-seq) in MBD3 knockdowned MCF-7 cells. We observed the decrease of nucleosome occupancy at promoters and enhancers in MBD3 knockdowned cells. Our results suggest a regulatory role of MBD3/NuRD at open chromatin region. Mapped nucleosome positioning in control (shLuc) and MBD3 knockdowned MCF-7 cells, in duplicate.
Project description:Previous studies indicate that eukaryotic promoters display a stereotypical chromatin landscape characterized by a well-positioned +1 nucleosome near the transcription start site and an upstream -1 nucleosome that together demarcate a nucleosome-free (or depleted) region. Here we present evidence that there are two distinct types of promoters distinguished by the resistance of the -1 nucleosome to micrococcal nuclease digestion. These different architectures are characterized by two sequence motifs that are broadly deployed at one set of promoters where a nuclease-sensitive ("fragile") nucleosome forms, but concentrated in a more narrow, nucleosome-free region at all other promoters. The RSC nucleosome remodeler acts through the motifs to establish stable +1 and -1 nucleosome positions, while binding of a small set of general regulatory (pioneer) factors at fragile nucleosome promoters plays a key role in their destabilization. We propose that the fragile nucleosome promoter architecture is adapted for regulation of highly expressed, growth-related genes. MNase-seq profiles obtained with various MNase concentrations from wild-type cells and cells depleted of different factors. ChIP-seq using anti-RNA polymerase II antibody, anti-histone H2A antibody, and anti-histone H3 antibody.
Project description:Histone H3K4 methylation is connected to gene transcription from yeast to humans, but its mechanistic role in transcription and chromatin dynamics remains poorly understood. Here, we investigated the functions for Set1 and Jhd2, the sole H3K4 methyltransferase and H3K4 demethylase, respectively, in S. cerevisiae. Our data show that Set1 and Jhd2 predominantly co-regulate transcription. We find combined activities of Set1 and Jhd2 via H3K4 methylation contribute to positive or negative transcriptional regulation at shared target genes. Providing mechanistic insights, our data reveal that Set1 and Jhd2 together control nucleosomal occupancy during transcriptional co-regulation. Moreover, we find a remarkable genome-wide co-regulation of nucleosome and chromatin structure by Set1 and Jhd2 at different groups of transcriptionally active or inactive genes and at different regions within yeast genes. Overall, our study prompts a model wherein combined actions of Set1 and Jhd2 via H3K4 methylationâdemethylation control chromatin dynamics during various facets of transcriptional regulation. Genome-wide nucleosome maps were generated from three different yeast strains representing wild type control, set1 null and jhd2 null mutants. Three independent biological samples were grown for each strain, nucleosomes were prepared by micrococcal nuclease digestion, libraries were prepared, mononculeosomal DNA was isolated, sequenced, and analyzed separately.
Project description:Knowing the exact positions of nucleosomes not only advances our understanding of their role in gene regulation, but also the mechanisms that underlie between-species variation in chromatin structure. We have generated a chemical map of nucleosomes in vivo in Schizosaccharomyces pombe at base pair resolution. This new map reveals that S.pombe genome shares a similar periodic linker length distribution with Saccharomyces cerevisiae, but with major distinctions in nucleosomal/linker DNA sequence features. In S.pombe, A/T rich sequences are enriched in the nucleosome core region, particularly +/-20 bp of dyad, while they are disfavored in S.cerevisiae nucleosomes. The poly (dA-dT) tracts only slightly affect the nucleosome occupancy in S.pombe; and they possess preferential rotational positions within the nucleosome core with significant enrichment in the 10-30 bp region from the dyad for longer tracts. S.pombe does not have well-defined nucleosome free region immediately upstream of most transcription start sites (TSS), instead the -1 nucleosome is positioned with regular distance to the +1 nucleosome, and its occupancy is negatively correlated with gene expression. The nucleosomes around TSS show more pronounced bidirectional phasing when the intergenic distance is relatively short, and the downstream nucleosome positioning is strongly correlated with DNA sequence features. We discovered that heterochromatin regions tend to have sparse nucleosome positioning, mixed with both well-positioned and fuzzy nucleosomes. The S.pombe map suggests that some of nucleosome positioning codes, formerly thought to be intrinsic, may largely depend on species-specific extrinsic factors including linker histone, chromatin remodelers and other DNA-binding proteins. 2 samples were analyzed with high throughput paired-end parallel sequencing. Both samples were created using the same chemical mapping protocol
Project description:When challenged with osmotic shock, S. cerevisiae induces hundreds of genes, despite a global reduction in transcriptional capacity. The mechanisms that regulate this rapid reallocation of transcriptional resources are not known. Here we show that redistribution of RNA Pol II upon stress requires the stress-responsive MAP kinase Hog1. We find that Hog1 and RNA Pol II co-localize to open reading frames that bypass global transcriptional repression, and that these targets are specified by two osmotic stress-responsive transcription factors. The combination of reduced global transcription with a gene-specific override mechanism allows cells to rapidly switch their transcriptional program in response to stress. ChIP-sequencing of S. cervisiae RNA Pol II, Hog1, Sko1 and Hot1 Processed data file descriptions: ORFcounts.txt: table of summed ChIP-seq reads that align to each ORF (normalized by reads per kilobase per million) promoter_counts.txt: table of summed ChIP-seq reads that align to each promoter (1kb upstream, normalized by reads per kilobase per million) downstream_counts.txt: table of summed ChIP-seq reads that align 3' regions (50-500 bp downstream, normalized by reads per kilobase per million) Sko1_peak_list.txt: table of peaks found by PeakSeq Hot1_peak_list.txt: table of peaks found by PeakSeq
Project description:To analyse nucleosome positioning and occupancy we performed micrococcal nuclease digestion of Arabidopsis wild type (Col-0) chromatin and gel purified the resulting ~150 bp mononucleosomal DNA band. This DNA was used to generate a library and paired-end sequencing performed (MNase-seq). To further examine influence of SWR1 chromatin remodelling complex and DNA methylation on nucleosome occupancy, we repeated MNase-seq in Aarabidopsis arp6 and met1 mutant.
Project description:The occupancy of nucleosomes governs access to the eukaryotic genomes and results from a combination of biophysical features and the effect of ATP-dependent remodeling complexes. Most promoter regions show a conserved pattern characterized by a nucleosome-depleted region (NDR) flanked by nucleosomal arrays. The conserved RSC remodeler was reported to be critical to establish NDR in vivo in budding yeast but other evidences suggested that this activity may not be conserved in fission yeast. By reanalysing and expanding previously published data, we propose that NDR formation is dependent on RSC in both yeast species. We also discuss the most prominent biological role of RSC and the possibility that non-essential subunits define alternate versions of the complex. Samples from mononucleosomal DNA from S. pombe strains h- kanR-tetO-snf21-Tap-natR ura4::rTetR-tup11 were sequenced (Illumina NextSeq 500 platform) using the pair-end read protocol