Readers of histone modifications.
Ontology highlight
ABSTRACT:
SUBMITTER: Yun M
PROVIDER: S-EPMC3131977 | biostudies-literature |
REPOSITORIES: biostudies-literature
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Project description:Transcription in eukaryotes is associated with two major changes in chromatin organization. Firstly, nucleosomal histones are continuously replaced by new histones, an event that in yeast occurs predominantly at transcriptionally active promoters. Secondly, histones become modified post-translationally at specific lysine residues. Some modifications, including histone H3 trimethylation at lysine 4 (H3K4me3) and acetylation at lysines 9 (H3K9ac) and 14 (H3K14ac), are specifically enriched at active promoters where histones exchange, suggesting a possible causal relationship. Other modifications accumulate within transcribed regions and one of them, H3K36me3, is thought to prevent histone exchange. Here we explored the relationship between these four H3 modifications and histone turnover at a few selected genes. Using lysine-to-arginine mutants and a histone exchange assay, we found that none of these modifications plays a major role in either promoting or preventing histone turnover. Unexpectedly, mutation of H3K56, whose acetylation occurs prior to chromatin incorporation, had an effect only when introduced into the nucleosomal histone. Furthermore, we used various genetic approaches to show that histone turnover can be experimentally altered with no major consequence on the H3 modifications tested. Together, these results suggest that transcription-associated histone turnover and H3 modification are two correlating but largely independent events.
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Project description:Chromatin is not an inert structure, but rather an instructive DNA scaffold that can respond to external cues to regulate the many uses of DNA. A principle component of chromatin that plays a key role in this regulation is the modification of histones. There is an ever-growing list of these modifications and the complexity of their action is only just beginning to be understood. However, it is clear that histone modifications play fundamental roles in most biological processes that are involved in the manipulation and expression of DNA. Here, we describe the known histone modifications, define where they are found genomically and discuss some of their functional consequences, concentrating mostly on transcription where the majority of characterisation has taken place.
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Project description:BackgroundChromatin, residing in the nuclei of eukaryotic cells, comprises DNA and histones to make up chromosomes. Chromatin condenses to compact the chromosomes and loosens to facilitate gene transcription and DNA replication/repair. Chemical modifications to the histones mediate changes in chromatin structure. Histone-modifying enzymes are potential drug targets. How herbs affect phenotypes through histone modifications is interesting.MethodsTwo public traditional Chinese medicine (TCM) databases were accessed to retrieve the chemical constituents and TCM natures of 3,294 TCM medicinals. NCBI taxonomy database was accessed to build the phylogenetic tree of the TCM medicinals. Statistical test was used to test if TCM natures of the medicinals cluster in the phylogenetic tree. A public chemical-protein interaction database was accessed to identify TCM medicinals whose constituent chemicals interact with human histone-modifying enzymes. For each histone modification, a correlation coefficient was calculated between the medicinals' TCM natures and modification modulabilities. Information of the ingredient medicinals of 200 classical TCM formulas was accessed from a public database.ResultsIt was found that 1,170 or 36% of the 3,294 TCM medicinals interact with human histone-modifying enzymes. Among the histone-modifying medicinals, 56% of them promote chromatin condensation. The cold-hot natures of TCM medicinals were found to be phylogenetically correlated. Furthermore, cold (hot) TCM medicinals were found to be associated with heterochromatinization (euchromatinization) through mainly H3K9 methylation and H3K4 demethylation. The associations were weak yet statistically significant. On the other hand, analysis of TCM formulas, the major form of TCM prescriptions in clinical practice, found that 99% of 200 government approved TCM formulas are histone-modifying. Furthermore, in formula formation, heterochromatic medicinals were found to team up with other heterochromatic medicinals to enhance the heterochromatinization of the formula. The synergy was mainly through concurrent DNMT and HDAC inhibition, co-inhibition of histone acetylation and H3S10 phosphorylation, or co-inhibition of H3K4 demethylation and H3K36 demethylation.ConclusionsTCM prescriptions' modulation of the human epigenome helps elucidation of phyto-pharmacology and discovery of epigenetic drugs. Furthermore, as TCM medicinals' properties are closely tied to patient TCM syndromes, results of this materia-medica-wide, bioinformatic analysis of TCM medicinals may have implications for molecular differentiation of TCM syndromes.
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Project description:Histones form the protein core around which genomic DNA is wrapped in eukaryotic chromatin. Numerous genetic studies have established that the structure and transcriptional state of chromatin are closely related to histone post-translational modifications. Further elucidation of the precise mechanistic roles for individual histone modifications requires the ability to isolate and study homogeneously modified histones. However, the highly heterogeneous nature of histone modifications in vivo poses a significant challenge for such studies. Chemical tools that have enabled biochemical and biophysical studies of site-specifically modified histones are the focus of this minireview.
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Project description:Histones undergo numerous covalent modifications that play important roles in regulating gene expression. Previous investigations have focused on the effects of histone modifications on gene promoters, whereas efforts to unravel their effects on transcribed regions have lagged behind. To elucidate the effects of histone modification on transcribed regions, we constructed a quantitative model, which we suggest can predict the variation of gene expression more faithfully than the model constructed on promoters. Moreover, motivated by the fact that exon spicing is functionally coupled to transcription, we also devised a quantitative model to predict alternative exon expression using histone modifications on exons. This model was found to be general across different exon types and even cell types. Furthermore, an interaction network linking histone modifications to alternative exon expression was constructed using partial correlations. The network indicated that gene expression and specific histone modifications (H3K36me3 and H4K20me1) could directly influence the exon expression, while other modifications could act in an additive way to account for the stability and robustness. In addition, our results suggest that combinations of histone modifications contribute to exon splicing in a redundant and cumulative fashion. To conclude, this study provides a better understanding of the effects of histone modifications on gene transcribed regions.
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