Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: UNIPROT:P06889 (Mol)
 630,302 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Although methods for light microscopy of chromatin are well established, there are no quantitative data for nucleosome concentrations in vivo. To establish such a method we used a HeLa clone expressing the core histone H2B fused to the enhanced yellow fluorescent protein (H2B-EYFP). Quantitative gel electrophoresis and fluorescence correlation spectroscopy (FCS) of isolated oligonucleosomes show that 5% of the total H2Bs carry the fluorescent tag and an increased nucleosome repeat length of 204 bp for the fluorescent cells. In vivo, the mobility and distribution of H2B-EYFP were studied with a combination of FCS and confocal imaging. With FCS, concentration and brightness of nascent molecules were measured in the cytoplasm, while in the nucleoplasm a background of mobile fluorescent histones was determined by continuous photobleaching. Combining these results allows converting confocal fluorescence images of nuclei into calibrated nucleosome density maps. Absolute nucleosome concentrations in interphase amount up to 250 microM locally, with mean values of 140(+/-28)microM, suggesting that a condensation-controlled regulation of site accessibility takes place at length scales well below 200 nm.
J Mol Biol 2003 Nov 21
PMID:Counting nucleosomes in living cells with a combination of fluorescence correlation spectroscopy and confocal imaging. 1460 15

In Saccharomyces cerevisiae, methylation of histone H3 at active genes is an epigenetic mark that distinguishes active from silent chromatin and functions as a short-term "memory" of recent transcription. Methylation of H3 at lysine residues K4 and K79 depends on ubiquitylation of histone H2B, but the mechanisms linking H2B ubiquitylation to H3 methylation are unknown. Here, we demonstrate that proteasomal ATPases Rpt4 and Rpt6 function to connect these two histone modifications. We show that recruitment of proteasome subunits to chromatin depends on H2B ubiquitylation and that mutations in Rpt4 and Rpt6 disrupt H3 methylation at K4 and K79 but leave H2B ubiquitylation intact. Consistent with their role in H3 methylation, we also find that mutations in Rpt4 and 6-but not components of the 20S proteasome-disrupt telomeric gene silencing. These data reveal that proteasome subunits function in epigenetic gene regulation by linking chromatin modifications that establish the histone code.
Mol Cell 2004 Feb 13
PMID:Proteasomal ATPases link ubiquitylation of histone H2B to methylation of histone H3. 1496 50

This work describes the nature and sequence information content of the electron capture dissociation mass spectra for the intact Tetrahymena histone H2B. Two major variants of this protein were present bearing nominal modifications of both +42 and +84 Da. This work describes identification of the nature of these two modifications. For example, using gas-phase selection and isolation of the +42-Da modified species, from a background of two H2B variants each present in six or more posttranslationally modified isoforms, we were able to determine that this +42-Da modification isoform bears trimethylation rather than acetylation. LC-CIDMS analysis was also employed on digested preparations to obtain complementary detail of the nature of site-specific posttranslational modifications. This study establishes that integration of the information from these two datasets provides a comprehensive map of posttranslational occupancy for each particular covalent assemblage selected for structural investigation.
Mol Cell Proteomics 2004 Sep
PMID:Characterization of Tetrahymena histone H2B variants and posttranslational populations by electron capture dissociation (ECD) Fourier transform ion cyclotron mass spectrometry (FT-ICR MS). 1519 21

Histone modifications play a pivotal role in regulating transcription and other chromatin-associated processes. In yeast, histone H2B monoubiquitylation affects gene silencing. However, mammalian histone ubiquitylation remains poorly understood. We report that the Mdm2 oncoprotein, a RING domain E3 ubiquitin ligase known to ubiquitylate the p53 tumor suppressor protein, can interact directly with histones and promote in vitro monoubiquitylation of histones H2A and H2B. Moreover, Mdm2 induces H2B monoubiquitylation in vivo. Endogenous Mdm2 is tethered in vivo, presumably via p53, to chromatin comprising the p53-responsive p21(waf1) promoter, and Mdm2 overexpression enhances protein ubiquitylation in the vicinity of a p53 binding site within that promoter. Moreover, when recruited to a promoter in the absence of p53, Mdm2 can repress transcription dependently on its RING domain, suggesting that its E3 activity contributes to repression. Histone ubiquitylation may thus constitute a novel mechanism of transcriptional repression by Mdm2, possibly underlying some of its oncogenic activities.
Mol Cell 2004 Nov 19
PMID:The RING domain of Mdm2 mediates histone ubiquitylation and transcriptional repression. 1554 22

We show that the three core histones H2A, H3 and H4 can transverse lipid bilayers of large unilamellar vesicles (LUVs) and multilamellar vesicles (MLVs). In contrast, the histone H2B, although able to bind to the liposomes, fails to penetrate the unilamellar and the multilamellar vesicles. Translocation across the lipid bilayer was determined using biotin-labeled histones and an ELISA-based system. Following incubation with the liposomes, external membrane-bound biotin molecules were neutralized by the addition of avidin. Penetrating biotin-histone conjugates were exposed by Triton treatment of the neutralized liposomes. The intraliposomal biotin-histone conjugates, in contrast to those attached only to the external surface, were attached to the detergent lysed lipid molecules. Thus, biotinylated histone molecules that were exposed only following detergent treatment of the liposomes were considered to be located at the inner leaflet of the lipid bilayers. The penetrating histone molecules failed to mediate translocation of BSA molecules covalently attached to them. Translocation of the core histones, including H2B, was also observed across mycoplasma cell membranes. The extent of this translocation was inversely related to the degree of membrane cholesterol. The addition of cholesterol also reduced the extent of histone penetration into the MLVs. Although able to bind biotinylated histones, human erythrocytes, erythrocyte ghosts and Escherichia coli cells were impermeable to them. Based on the present and previous data histones appear to be characterized by the same features that characterize cell penetrating peptides and proteins (CPPs).
J Mol Biol 2005 Jan 14
PMID:Translocation of histone proteins across lipid bilayers and Mycoplasma membranes. 1557 30

The position of chromosomal neighborhoods in living cells was followed using three different methods for marking chromosomal domains occupying arbitrary locations in the nucleus; photobleaching of GFP-labeled histone H2B, local UV-marked DNA, and photobleaching of fluorescently labeled DNA. All methods revealed that global chromosomal organization can be reestablished through one cell division from mother to daughters. By simultaneously monitoring cell cycle stage in the cells in which relative chromosomal domain positions were tracked, we observed that chromosomal neighborhood organization is apparently lost in the early G1 phase of the cell cycle. However, the daughter cells eventually regain the general chromosomal organization pattern of their mothers, suggesting an active mechanism could be at play to reestablish chromosomal neighborhoods.
Mol Biol Cell 2005 Feb
PMID:Dynamics of relative chromosome position during the cell cycle. 1557 74

Rad6-mediated ubiquitylation of histone H2B at lysine 123 has been linked to transcriptional activation and the regulation of lysine methylation on histone H3. However, how Rad6 and H2B ubiquitylation contribute to the transcription and histone methylation processes is poorly understood. Here, we show that the Paf1 transcription elongation complex and the E3 ligase for Rad6, Bre1, mediate an association of Rad6 with the hyperphosphorylated (elongating) form of RNA polymerase II (Pol II). This association appears to be necessary for the transcriptional activities of Rad6, as deletion of various Paf1 complex members or Bre1 abolishes H2B ubiquitylation (ubH2B) and reduces the recruitment of Rad6 to the promoters and transcribed regions of active genes. Using the inducible GAL1 gene as a model, we find that the recruitment of Rad6 upon activation occurs rapidly and transiently across the gene and coincides precisely with the appearance of Pol II. Significantly, during GAL1 activation in an rtf1 deletion mutant, Rad6 accumulates at the promoter but is absent from the transcribed region. This fact suggests that Rad6 is recruited to promoters independently of the Paf1 complex but then requires this complex for entrance into the coding region of genes in a Pol II-associated manner. In support of a role for Rad6-dependent H2B ubiquitylation in transcription elongation, we find that ubH2B levels are dramatically reduced in strains bearing mutations of the Pol II C-terminal domain (CTD) and abolished by inactivation of Kin28, the serine 5 CTD kinase that promotes the transition from initiation to elongation. Furthermore, synthetic genetic array analysis reveals that the Rad6 complex interacts genetically with a number of known or suspected transcription elongation factors. Finally, we show that Saccharomyces cerevisiae mutants bearing defects in the pathway to H2B ubiquitylation display transcription elongation defects as assayed by 6-azauracil sensitivity. Collectively, our results indicate a role for Rad6 and H2B ubiquitylation during the elongation cycle of transcription and suggest a mechanism by which H3 methylation may be regulated.
Mol Cell Biol 2005 Jan
PMID:Histone H2B ubiquitylation is associated with elongating RNA polymerase II. 1563 65

Covalent modifications of the histone tails and the cross talk between these modifications are hallmark features of gene regulation. The SAGA histone acetyltransferase complex is one of the most well-characterized complexes involved in these covalent modifications. The recent finding that the removal of the ubiquitin group from H2B is performed by a component of SAGA, Ubp8, is intriguing as it assigns two posttranslation modification processes to one complex. In this work, we characterize the association of Ubp8 with SAGA and the effect that acetylation and deubiquitylation have on one another in vitro and in vivo. We found not only that Ubp8 is a part of the SAGA complex, but also that its deubiquitylation activity requires Ubp8's association with SAGA. Furthermore, we found that the Ubp8 association with SAGA requires Sgf11 and that this requirement is reciprocal. We also found that the acetylation and deubiquitylation activities of SAGA are independent of one another. However, we found that preacetylating histone H2B inhibited subsequent deubiquitylation. Additionally, we found that increasing the ubiquitylation state of H2B inhibited the expression of the ARG1 gene, whose repression was previously shown to require the RAD6 ubiquitin ligase. Taken together, these data indicate that the expression of some genes, including ARG1, is regulated by a balance of histone H2B ubiquitylation in the cell.
Mol Cell Biol 2005 Feb
PMID:The deubiquitylation activity of Ubp8 is dependent upon Sgf11 and its association with the SAGA complex. 1565 42

The packaging of eukaryotic genomic DNA into chromatin is modulated through a range of posttranslational histone modifications. Among these, the role of histone ubiquitylation remains poorly understood. Here, we show that the essential Drosophila ubiquitin-specific protease 7 (USP7) contributes to epigenetic silencing of homeotic genes by Polycomb (Pc). We purified USP7 from embryo nuclear extracts as a stable heteromeric complex with guanosine 5'-monophosphate synthetase (GMPS). The USP7-GMPS complex catalyzed the selective deubiquitylation of histone H2B, but not H2A. Biochemical assays confirmed the tight association between USP7 and GMPS in Drosophila embryo extracts. Similar to USP7, mutations in GMPS acted as enhancers of Pc in vivo. USP7 binding to GMPS was required for histone H2B deubiquitylation and strongly augmented deubiquitylation of the human tumor suppressor p53. Thus, GMPS can regulate the activity of a ubiquitin protease. Collectively, these results implicate a biosynthetic enzyme in chromatin control via ubiquitin regulation.
Mol Cell 2005 Mar 04
PMID:GMP synthetase stimulates histone H2B deubiquitylation by the epigenetic silencer USP7. 1574 19

We previously discovered that the ubiquitin protease Ubp10/Dot4p is important for telomeric silencing through its interaction with Sir4p. However, the mechanism of Ubp10p action was unknown. We now provide evidence that Ubp10p removes ubiquitin from histone H2B; cells with UBP10 deleted have increased steady-state levels of H2B ubiquitination. As a consequence, ubp10delta cells also have increased steady-state levels of histone H3 Lys4 and Lys79 methylation. Consistent with its role in silencing, Ubp10p is preferentially localized to silent chromatin where its ubiquitin protease activity maintains low levels of H3 Lys4 and Lys79 methylation to allow optimal Sir protein binding to telomeres and global telomeric silencing. The ubiquitin protease Ubp8p has also been shown to remove ubiquitin from H2B, and ubp8delta cells have increased steady-state levels of H2B ubiquitination similar to those in ubp10delta cells. Unlike ubp10delta cells, however, ubp8delta cells do not have increased steady-state levels of H3 Lys4 and Lys79 methylation, nor is telomeric silencing affected. Despite their separate functions in silencing and SAGA-mediated transcription, respectively, deletion of both UBP10 and UBP8 results in a synergistic increase in the steady-state levels of H2B ubiquitination and in the number of genes with altered expression, indicating that Ubp10p and Ubp8p likely overlap in some of their target chromatin regions. We propose that Ubp10p and Ubp8p are the only ubiquitin proteases that normally remove monoubiquitin from histone H2B and, while there are regions of the genome to which each is specifically targeted, both combine to regulate the global balance of H2B ubiquitination.
Mol Cell Biol 2005 Jul
PMID:Ubp10/Dot4p regulates the persistence of ubiquitinated histone H2B: distinct roles in telomeric silencing and general chromatin. 1598 24


<< Previous 1 2 3 4 5 6 7 8 9 10 Next >>