A fluorescent assay for cryptic transcription in Saccharomyces cerevisiae reveals novel insights into factors that stabilize chromatin structure on newly replicated DNA.

The disruption of chromatin structure can result in transcription initiation from cryptic promoters within gene bodies. While the passage of RNA polymerase II is a well-characterized chromatin-disrupting force, numerous factors, including histone chaperones, normally stabilize chromatin on transcribed genes, thereby repressing cryptic transcription. DNA replication, which employs a partially overlapping set of histone chaperones, is also inherently disruptive to chromatin, but a role for DNA replication in cryptic transcription has never been examined.

43rd International Asilomar Chromatin, Chromosomes, and Epigenetics Conference.

The 43rd Asilomar Chromatin, Chromosomes, and Epigenetics Conference was held in an entirely online format from 9 to 11 December 2021. The conference enabled presenters at various career stages to share promising new findings, and presentations covered modern chromatin research across an array of model systems. Topics ranged from the fundamental principles of nuclear organization and transcription regulation to key mechanisms underlying human disease.

Pterostilbene Changes Epigenetic Marks at Enhancer Regions of Oncogenes in Breast Cancer Cells.

Epigenetic aberrations are linked to sporadic breast cancer. Interestingly, certain dietary polyphenols with anti-cancer effects, such as pterostilbene (PTS), have been shown to regulate gene expression by altering epigenetic patterns. Our group has proposed the involvement of DNA methylation and DNA methyltransferase 3B (DNMT3B) as vital players in PTS-mediated suppression of candidate oncogenes and suggested a role of enhancers as target regions.

Pterostilbene leads to DNMT3B-mediated DNA methylation and silencing of OCT1-targeted oncogenes in breast cancer cells.

Transcription factor (TF)-mediated regulation of genes is often disrupted during carcinogenesis. The DNA methylation state of TF-binding sites may dictate transcriptional activity of corresponding genes. Stilbenoid polyphenols, such as pterostilbene (PTS), have been shown to exert anticancer action by remodeling DNA methylation and gene expression.

Transcription shapes genome-wide histone acetylation patterns.

Histone acetylation is a ubiquitous hallmark of transcription, but whether the link between histone acetylation and transcription is causal or consequential has not been addressed. Using immunoblot and chromatin immunoprecipitation-sequencing in S. cerevisiae, here we show that the majority of histone acetylation is dependent on transcription.

The Function and Evolution of Motile DNA Replication Systems in Ciliates.

DNA replication is a ubiquitous and conserved cellular process. However, regulation of DNA replication is only understood in a small fraction of organisms that poorly represent the diversity of genetic systems in nature. Here we used computational and experimental approaches to examine the function and evolution of one such system, the replication band (RB) in spirotrich ciliates, which is a localized, motile hub that traverses the macronucleus while replicating DNA.

Transcription Promotes the Interaction of the FAcilitates Chromatin Transactions (FACT) Complex with Nucleosomes in .

The FACT (FAcilitates Chromatin Transactions) complex is a conserved complex that maintains chromatin structure on transcriptionally active genes. Consistent with this, FACT is enriched on highly expressed genes, but how it is targeted to these regions is unknown. , FACT binds destabilized nucleosomes, supporting the hypothesis that FACT is targeted to transcribed chromatin through recognition of RNA polymerase (RNAP)-disrupted nucleosomes.

Viral proteins as a potential driver of histone depletion in dinoflagellates.

Within canonical eukaryotic nuclei, DNA is packaged with highly conserved histone proteins into nucleosomes, which facilitate DNA condensation and contribute to genomic regulation. Yet the dinoflagellates, a group of unicellular algae, are a striking exception to this otherwise universal feature as they have largely abandoned histones and acquired apparently viral-derived substitutes termed DVNPs (dinoflagellate-viral-nucleoproteins). Despite the magnitude of this transition, its evolutionary drivers remain unknown.

Histone Acetylation, Not Stoichiometry, Regulates Linker Histone Binding in .

Linker histones play a fundamental role in shaping chromatin structure, but how their interaction with chromatin is regulated is not well understood. In this study, we used a combination of genetic and genomic approaches to explore the regulation of linker histone binding in the yeast, We found that increased expression of Hho1, the yeast linker histone, resulted in a severe growth defect, despite only subtle changes in chromatin structure. Further, this growth defect was rescued by mutations that increase histone acetylation.

Histone H3K4 and H3K36 Methylation Independently Recruit the NuA3 Histone Acetyltransferase in .

Histone post-translational modifications (PTMs) alter chromatin structure by promoting the interaction of chromatin-modifying complexes with nucleosomes. The majority of chromatin-modifying complexes contain multiple domains that preferentially interact with modified histones, leading to speculation that these domains function in concert to target nucleosomes with distinct combinations of histone PTMs. In , the NuA3 histone acetyltransferase complex contains three domains, the PHD finger in Yng1, the PWWP domain in Pdp3, and the YEATS domain in Taf14; which bind to H3K4 methylation, H3K36 methylation, and acetylated and crotonylated H3K9, respectively.

Divergent Residues Within Histone H3 Dictate a Unique Chromatin Structure in Saccharomyces cerevisiae.

Histones are among the most conserved proteins known, but organismal differences do exist. In this study, we examined the contribution that divergent amino acids within histone H3 make to cell growth and chromatin structure in Saccharomyces cerevisiae. We show that, while amino acids that define histone H3.

Polarization of the endoplasmic reticulum by ER-septin tethering.

Polarization of the plasma membrane (PM) into domains is an important mechanism to compartmentalize cellular activities and to establish cell polarity. Polarization requires formation of diffusion barriers that prevent mixing of proteins between domains. Recent studies have uncovered that the endoplasmic reticulum (ER) of budding yeast and neurons is polarized by diffusion barriers, which in neurons controls glutamate signaling in dendritic spines.

Histone H3K4 demethylation is negatively regulated by histone H3 acetylation in Saccharomyces cerevisiae.

Histone H3 lysine 4 trimethylation (H3K4me3) is a hallmark of transcription initiation, but how H3K4me3 is demethylated during gene repression is poorly understood. Jhd2, a JmjC domain protein, was recently identified as the major H3K4me3 histone demethylase (HDM) in Saccharomyces cerevisiae. Although JHD2 is required for removal of methylation upon gene repression, deletion of JHD2 does not result in increased levels of H3K4me3 in bulk histones, indicating that this HDM is unable to demethylate histones during steady-state conditions.

Critical determinants for chromatin binding by Saccharomyces cerevisiae Yng1 exist outside of the plant homeodomain finger.

The temporal and spatial regulation of histone post-translational modifications is essential for proper chromatin structure and function. The Saccharomyces cerevisiae NuA3 histone acetyltransferase complex modifies the amino-terminal tail of histone H3, but how NuA3 is targeted to specific regions of the genome is not fully understood. Yng1, a subunit of NuA3 and a member of the Inhibitor of Growth (ING) protein family, is required for the interaction of NuA3 with chromatin.

Histone acetylation: where to go and how to get there.

Transcriptionally active DNA is packaged with histones that are post-translationally acetylated on multiple lysines within their amino termini. While the majority of this acetylation is limited to the promoters of genes, acetylated histones are also found throughout transcribed units. Over the last decade we have uncovered many of the pathways involved in directing histone acetylation to active genes.

Histone acetylation: truth of consequences?

Eukaryotic DNA is packaged into a nucleoprotein structure known as chromatin, which is comprised of DNA, histones, and nonhistone proteins. Chromatin structure is highly dynamic, and can shift from a transcriptionally inactive state to an active form in response to intra- and extracellular signals. A major factor in chromatin architecture is the covalent modification of histones through the addition of chemical moieties, such as acetyl, methyl, ubiquitin, and phosphate groups.

Acetylation of Rsc4p by Gcn5p is essential in the absence of histone H3 acetylation.

Rsc4p, a subunit of the RSC chromatin-remodeling complex, is acetylated at lysine 25 by Gcn5p, a well-characterized histone acetyltransferase (HAT). Mutation of lysine 25 does not result in a significant growth defect, and therefore whether this modification is important for the function of the essential RSC complex was unknown. In a search to uncover the molecular basis for the lethality resulting from loss of multiple histone H3-specific HATs, we determined that loss of Rsc4p acetylation is lethal in strains lacking histone H3 acetylation.