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Rebecca Kellum - One of the best experts on this subject based on the ideXlab platform.
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mutations in the Heterochromatin Protein 1 hp1 hinge domain affect hp1 Protein interactions and chromosomal distribution
Chromosoma, 2005Co-Authors: Ramakrishna Badugu, Prim B Singh, Youngdong Yoo, Rebecca KellumAbstract:Heterochromatin Protein 1 (HP1) is a conserved component of the highly compact chromatin found at centromeres and telomeres. A conserved feature of the Protein is multiple phosphorylation. Hyper-phosphorylation of HP1 accompanies the assembly of cytologically distinct Heterochromatin during early embryogenesis. Hypo-phosphorylated HP1 is associated with the DNA-binding activities of the origin recognition complex (ORC) and an HMG-like HP1/ORC-Associated Protein (HOAP). Perturbations in HP1 localization in pericentric and telomeric Heterochromatin in mutants for Drosophila ORC2 and HOAP, respectively, indicate roles for these HP1 phosphoisoforms in Heterochromatin assembly also. To elucidate the roles of hypo- and hyper-phosphophorylated HP1 in Heterochromatin assembly, we have mutated consensus Protein Kinase-A phosphorylation sites in the HP1 hinge domain and examined the mutant Proteins for distinct in vitro and in vivo activities. Mutations designed to mimic hyper-phosphorylation render the Protein incapable of binding HOAP and the DmORC1 subunit but confer enhanced homo-dimerization and lysine 9-methylated histone H3-binding to the Protein. Mutations rendering the Protein unphosphorylatable, by contrast, do not affect homo-dimerization or binding to lysine 9-di-methylated histone H3, HOAP, or DmORC1 but do confer novel DmORC2-binding activity to the Protein. This mutant Protein is ectopically localized throughout the chromosomes when overexpressed in vivo in the presence of a full dose of DmORC2. This ectopic targeting is accompanied by ectopic targeting of lysine 9 tri-methylated histone H3. The distinct activities of these mutant Proteins could reflect distinct roles for HP1 phosphoisoforms in Heterochromatin structure and function.
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novel drosophila Heterochromatin Protein 1 hp1 origin recognition complex associated Protein hoap repeat motif in hp1 hoap interactions and chromocenter associations
Journal of Biological Chemistry, 2003Co-Authors: Ramakrishna Badugu, Mohammed M Shareef, Rebecca KellumAbstract:Association of the highly conserved Heterochromatin Protein, HP1, with the specialized chromatin of centromeres and telomeres requires binding to a specific histone H3 modification of methylation on lysine 9. This modification is catalyzed by the Drosophila Su(var)3-9 gene product and its homologues. Specific DNA binding activities are also likely to be required for targeting this activity along with HP1 to specific chromosomal regions. The Drosophila HOAP Protein is a DNA-binding Protein that was identified as a component of a multiProtein complex of HP1 containing Drosophila origin recognition complex (ORC) subunits in the early Drosophila embryo. Here we show direct physical interactions between the HOAP Protein and HP1 and specific ORC subunits. Two additional HP1-like Proteins (HP1b and HP1c) were recently identified in Drosophila, and the unique chromosomal distribution of each isoform is determined by two independently acting HP1 domains (hinge and chromoshadow domain) (47). We find Heterochromatin Protein 1/origin recognition complex-associated Protein (HOAP) to interact specifically with the originally described predominantly heterochromatic HP1a Protein. Both the hinge and chromoshadow domains of HP1a are required for its interaction with HOAP, and a novel peptide repeat located in the carboxyl terminus of the HOAP Protein is required for the interaction with the HP1 hinge domain. Peptides that interfere with HP1a/HOAP interactions in co-precipitation experiments also displace HP1 from the heterochromatic chromocenter of polytene chromosomes in larval salivary glands. A mutant for the HOAP Protein also suppresses centric Heterochromatin-induced silencing, supporting a role for HOAP in centric Heterochromatin.
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drosophila Heterochromatin Protein 1 hp1 origin recognition complex orc Protein is associated with hp1 and orc and functions in Heterochromatin induced silencing
Molecular Biology of the Cell, 2001Co-Authors: Mohammed M Shareef, Chadwick King, Mona Damaj, Ramakrishna Badagu, Da Wei Huang, Rebecca KellumAbstract:Heterochromatin Protein 1 (HP1) is a conserved component of the highly compact chromatin of higher eukaryotic centromeres and telomeres. Cytogenetic experiments in Drosophila have shown that HP1 localization into this chromatin is perturbed in mutants for the origin recognition complex (ORC) 2 subunit. ORC has a multisubunit DNA-binding activity that binds origins of DNA replication where it is required for origin firing. The DNA-binding activity of ORC is also used in the recruitment of the Sir1 Protein to silence nucleation sites flanking silent copies of the mating-type genes in Saccharomyces cerevisiae. A fraction of HP1 in the maternally loaded cytoplasm of the early Drosophila embryo is associated with a multiProtein complex containing Drosophila melanogaster ORC subunits. This complex appears to be poised to function in Heterochromatin assembly later in embryonic development. Here we report the identification of a novel component of this complex, the HP1/ORC-associated Protein. This Protein contains similarity to DNA sequence-specific HMG Proteins and is shown to bind specific satellite sequences and the telomere-associated sequence in vitro. The Protein is shown to have heterochromatic localization in both diploid interphase and mitotic chromosomes and polytene chromosomes. Moreover, the gene encoding HP1/ORC-associated Protein was found to display reciprocal dose-dependent variegation modifier phenotypes, similar to those for mutants in HP1 and the ORC 2 subunit.
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Heterochromatin Protein 1 distribution during development and during the cell cycle in drosophila embryos
Journal of Cell Science, 1995Co-Authors: Rebecca Kellum, Jordan W Raff, Bruce AlbertsAbstract:Heterochromatin Protein 1 (HP1) was initially discovered as a Protein that is associated with the Heterochromatin at the chromocenter of polytene chromosomes in Drosophila larval salivary glands. In this paper we investigate the localization of Heterochromatin Protein 1 in the diploid nuclei of Drosophila embryos. We focus on its association with the interphase Heterochromatin in fixed embryos before and during cycle 14, the developmental time at which Heterochromatin becomes most conspicuous, and also follow its localization during mitosis. The GAGA transcription factor was recently shown to be localized at sequences within alpha-Heterochromatin in pre-cycle 14 embryos, and an antibody against this Protein serves as a convenient marker for these sequences. We find an enrichment of Heterochromatin Protein 1 in the intensely DAPI-staining regions near the apical surface of nuclear cycle 10 embryos. At this stage GAGA factor is localized into punctate structures in this same region. This enrichment for HP1 is markedly increased during nuclear cycle 14. Surprisingly, whereas GAGA factor retains its association with the Heterochromatin throughout the cell cycle, a significant fraction of HP1 is dispersed throughout the spindle around the segregating chromosomes during mitosis. This dispersed pool of Heterochromatin Protein 1 was observed during mitosis in both early and late Drosophila embryos and in an analysis of a bacterially produced 6x histidine-Heterochromatin Protein 1 fusion Protein injected into living Drosophila embryos. When Drosophila tissue culture cells were prepared by a method which removes soluble Protein and avoids fixation of the mitotic chromosomes, an enrichment for Heterochromatin Protein 1 in the Heterochromatin of the chromosomes was discovered also.
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Heterochromatin Protein 1 is required for correct chromosome segregation in drosophila embryos
Journal of Cell Science, 1995Co-Authors: Rebecca Kellum, Bruce AlbertsAbstract:Heterochromatin Protein 1 is associated with centromeric Heterochromatin in Drosophila, mice, and humans. Loss of function mutations in the gene encoding Heterochromatin Protein 1 in Drosophila, Suppressor of variegation2-5, decrease the mosaic repression observed for euchromatic genes that have been juxtaposed to centromeric Heterochromatin. These Heterochromatin Protein 1 mutations not only suppress this position-effect variegation, but also cause recessive embryonic lethality. In this study, we analyze the latter phenotype in the hope of gaining insight into Heterochromatin function. In our analyses of four alleles of Suppressor of variegation2-5, the lethality was found to be associated with defects in chromosome morphology and segregation. While some of these defects are seen throughout embryonic development, both the frequency and severity of the defects are greatest between cycles 10 and 14 when zygotic transcription of the Suppressor of variegation2-5 gene apparently begins. By this time in development, Heterochromatin Protein 1 levels are diminished by four-fold in a quarter of the embryos produced by parents that are both heterozygous for a null allele (Suppressor of variegation2-5(05)). In a live analysis of the phenotype, we find prophase to be lengthened by more than two-fold in Suppressor of variegation2-5(05) mutant embryos with subsequent defects in chromosome segregation. The elongated prophase suggests that the segregation phenotype is a consequence of defects in events that occur during prophase, either in chromosome condensation or kinetochore assembly or function. Immunostaining with an antibody against a centromerespecific antigen indicates that the kinetochores of most chromosomes are functional. The immunostaining results are more consistent with defects in chromosome condensation being responsible for the segregation phenotype.
Koji Goto - One of the best experts on this subject based on the ideXlab platform.
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epigenetic maintenance of the vernalized state in arabidopsis thaliana requires like Heterochromatin Protein 1
Nature Genetics, 2006Co-Authors: Sibum Sung, Kenji Nakahigashi, Koji Goto, Yuehui He, Tifani W Eshoo, Yosuke Tamada, Lianna M Johnson, Steve E Jacobsen, Richard M AmasinoAbstract:Epigenetic maintenance of the vernalized state in Arabidopsis thaliana requires LIKE Heterochromatin Protein 1
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epigenetic maintenance of the vernalized state in arabidopsis thaliana requires like Heterochromatin Protein 1
Nature Genetics, 2006Co-Authors: Sibum Sung, Kenji Nakahigashi, Koji Goto, Tifani W Eshoo, Yosuke Tamada, Lianna M Johnson, Steve E Jacobsen, Richard M AmasinoAbstract:Vernalization is the process by which sensing a prolonged exposure to winter cold leads to competence to flower in the spring. In winter annual Arabidopsis thaliana accessions, flowering is suppressed in the fall by expression of the potent floral repressor FLOWERING LOCUS C (FLC). Vernalization promotes flowering via epigenetic repression of FLC. Repression is accompanied by a series of histone modifications of FLC chromatin that include dimethylation of histone H3 at Lys9 (H3K9) and Lys27 (H3K27). Here, we report that A. thaliana LIKE Heterochromatin Protein 1 (LHP1) is necessary to maintain the epigenetically repressed state of FLC upon return to warm conditions typical of spring. LHP1 is enriched at FLC chromatin after prolonged exposure to cold, and LHP1 activity is needed to maintain the increased levels of H3K9 dimethylation at FLC chromatin that are characteristic of the vernalized state.
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arabidopsis terminal flower 2 gene encodes a Heterochromatin Protein 1 homolog and represses both flowering locus t to regulate flowering time and several floral homeotic genes
Plant and Cell Physiology, 2003Co-Authors: Toshihisa Kotake, Shinobu Takada, Kenji Nakahigashi, Masaaki Ohto, Koji GotoAbstract:;Floral transition should be strictly regulated because it is one of the most critical developmental processes in plants. Arabidopsis terminal flower 2 (tfl2) mutants show an early-flowering phenotype that is relatively insensitive to photoperiod, as well as several other pleiotropic phenotypes. We found that the early flowering of tfl2 is caused mainly by ectopic expression of the FLOWERING LOCUS T (FT) gene, a floral pathway integrator. Molecular cloning of TFL2 showed that it encodes a Protein with homology to Heterochromatin Protein 1 (HP1) of animals and Swi6 of fission yeast. TFL2 Protein localizes in subnuclear foci and expression of the TFL2 gene complemented yeast swi6 – mutants. These results suggested that TFL2 might function as an HP1 in Arabidopsis. Gene expression analyses using DNA microarrays, however, did not show an increase in the expression of Heterochromatin genes in tfl2 mutants but instead showed the upregulation of the floral homeotic genes APETALA3, PISTILLATA, AGAMOUS and SEPALLATA3. The pleiotropic phenotype of the tfl2 mutant could reflect the fact that TFL2 represses the expression of multiple genes. Our results demonstrate that despite its homology to HP1, TFL2 is involved in the repression of specific euchromatin genes and not Heterochromatin genes in Arabidopsis.
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arabidopsis terminal flower 2 gene encodes a Heterochromatin Protein 1 homolog and represses both flowering locus t to regulate flowering time and several floral homeotic genes
Plant and Cell Physiology, 2003Co-Authors: Toshihisa Kotake, Shinobu Takada, Kenji Nakahigashi, Masaaki Ohto, Koji GotoAbstract:Floral transition should be strictly regulated because it is one of the most critical developmental processes in plants. Arabidopsis terminal flower 2 (tfl2) mutants show an early-flowering phenotype that is relatively insensitive to photoperiod, as well as several other pleiotropic phenotypes. We found that the early flowering of tfl2 is caused mainly by ectopic expression of the FLOWERING LOCUS T (FT) gene, a floral pathway integrator. Molecular cloning of TFL2 showed that it encodes a Protein with homology to Heterochromatin Protein 1 (HP1) of animals and Swi6 of fission yeast. TFL2 Protein localizes in subnuclear foci and expression of the TFL2 gene complemented yeast swi6(-) mutants. These results suggested that TFL2 might function as an HP1 in Arabidopsis: Gene expression analyses using DNA microarrays, however, did not show an increase in the expression of Heterochromatin genes in tfl2 mutants but instead showed the upregulation of the floral homeotic genes APETALA3, PISTILLATA, AGAMOUS and SEPALLATA3. The pleiotropic phenotype of the tfl2 mutant could reflect the fact that TFL2 represses the expression of multiple genes. Our results demonstrate that despite its homology to HP1, TFL2 is involved in the repression of specific euchromatin genes and not Heterochromatin genes in Arabidopsis.
Kenji Nakahigashi - One of the best experts on this subject based on the ideXlab platform.
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epigenetic maintenance of the vernalized state in arabidopsis thaliana requires like Heterochromatin Protein 1
Nature Genetics, 2006Co-Authors: Sibum Sung, Kenji Nakahigashi, Koji Goto, Yuehui He, Tifani W Eshoo, Yosuke Tamada, Lianna M Johnson, Steve E Jacobsen, Richard M AmasinoAbstract:Epigenetic maintenance of the vernalized state in Arabidopsis thaliana requires LIKE Heterochromatin Protein 1
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epigenetic maintenance of the vernalized state in arabidopsis thaliana requires like Heterochromatin Protein 1
Nature Genetics, 2006Co-Authors: Sibum Sung, Kenji Nakahigashi, Koji Goto, Tifani W Eshoo, Yosuke Tamada, Lianna M Johnson, Steve E Jacobsen, Richard M AmasinoAbstract:Vernalization is the process by which sensing a prolonged exposure to winter cold leads to competence to flower in the spring. In winter annual Arabidopsis thaliana accessions, flowering is suppressed in the fall by expression of the potent floral repressor FLOWERING LOCUS C (FLC). Vernalization promotes flowering via epigenetic repression of FLC. Repression is accompanied by a series of histone modifications of FLC chromatin that include dimethylation of histone H3 at Lys9 (H3K9) and Lys27 (H3K27). Here, we report that A. thaliana LIKE Heterochromatin Protein 1 (LHP1) is necessary to maintain the epigenetically repressed state of FLC upon return to warm conditions typical of spring. LHP1 is enriched at FLC chromatin after prolonged exposure to cold, and LHP1 activity is needed to maintain the increased levels of H3K9 dimethylation at FLC chromatin that are characteristic of the vernalized state.
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arabidopsis terminal flower 2 gene encodes a Heterochromatin Protein 1 homolog and represses both flowering locus t to regulate flowering time and several floral homeotic genes
Plant and Cell Physiology, 2003Co-Authors: Toshihisa Kotake, Shinobu Takada, Kenji Nakahigashi, Masaaki Ohto, Koji GotoAbstract:;Floral transition should be strictly regulated because it is one of the most critical developmental processes in plants. Arabidopsis terminal flower 2 (tfl2) mutants show an early-flowering phenotype that is relatively insensitive to photoperiod, as well as several other pleiotropic phenotypes. We found that the early flowering of tfl2 is caused mainly by ectopic expression of the FLOWERING LOCUS T (FT) gene, a floral pathway integrator. Molecular cloning of TFL2 showed that it encodes a Protein with homology to Heterochromatin Protein 1 (HP1) of animals and Swi6 of fission yeast. TFL2 Protein localizes in subnuclear foci and expression of the TFL2 gene complemented yeast swi6 – mutants. These results suggested that TFL2 might function as an HP1 in Arabidopsis. Gene expression analyses using DNA microarrays, however, did not show an increase in the expression of Heterochromatin genes in tfl2 mutants but instead showed the upregulation of the floral homeotic genes APETALA3, PISTILLATA, AGAMOUS and SEPALLATA3. The pleiotropic phenotype of the tfl2 mutant could reflect the fact that TFL2 represses the expression of multiple genes. Our results demonstrate that despite its homology to HP1, TFL2 is involved in the repression of specific euchromatin genes and not Heterochromatin genes in Arabidopsis.
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arabidopsis terminal flower 2 gene encodes a Heterochromatin Protein 1 homolog and represses both flowering locus t to regulate flowering time and several floral homeotic genes
Plant and Cell Physiology, 2003Co-Authors: Toshihisa Kotake, Shinobu Takada, Kenji Nakahigashi, Masaaki Ohto, Koji GotoAbstract:Floral transition should be strictly regulated because it is one of the most critical developmental processes in plants. Arabidopsis terminal flower 2 (tfl2) mutants show an early-flowering phenotype that is relatively insensitive to photoperiod, as well as several other pleiotropic phenotypes. We found that the early flowering of tfl2 is caused mainly by ectopic expression of the FLOWERING LOCUS T (FT) gene, a floral pathway integrator. Molecular cloning of TFL2 showed that it encodes a Protein with homology to Heterochromatin Protein 1 (HP1) of animals and Swi6 of fission yeast. TFL2 Protein localizes in subnuclear foci and expression of the TFL2 gene complemented yeast swi6(-) mutants. These results suggested that TFL2 might function as an HP1 in Arabidopsis: Gene expression analyses using DNA microarrays, however, did not show an increase in the expression of Heterochromatin genes in tfl2 mutants but instead showed the upregulation of the floral homeotic genes APETALA3, PISTILLATA, AGAMOUS and SEPALLATA3. The pleiotropic phenotype of the tfl2 mutant could reflect the fact that TFL2 represses the expression of multiple genes. Our results demonstrate that despite its homology to HP1, TFL2 is involved in the repression of specific euchromatin genes and not Heterochromatin genes in Arabidopsis.
Richard M Amasino - One of the best experts on this subject based on the ideXlab platform.
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epigenetic maintenance of the vernalized state in arabidopsis thaliana requires like Heterochromatin Protein 1
Nature Genetics, 2006Co-Authors: Sibum Sung, Kenji Nakahigashi, Koji Goto, Yuehui He, Tifani W Eshoo, Yosuke Tamada, Lianna M Johnson, Steve E Jacobsen, Richard M AmasinoAbstract:Epigenetic maintenance of the vernalized state in Arabidopsis thaliana requires LIKE Heterochromatin Protein 1
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epigenetic maintenance of the vernalized state in arabidopsis thaliana requires like Heterochromatin Protein 1
Nature Genetics, 2006Co-Authors: Sibum Sung, Kenji Nakahigashi, Koji Goto, Tifani W Eshoo, Yosuke Tamada, Lianna M Johnson, Steve E Jacobsen, Richard M AmasinoAbstract:Vernalization is the process by which sensing a prolonged exposure to winter cold leads to competence to flower in the spring. In winter annual Arabidopsis thaliana accessions, flowering is suppressed in the fall by expression of the potent floral repressor FLOWERING LOCUS C (FLC). Vernalization promotes flowering via epigenetic repression of FLC. Repression is accompanied by a series of histone modifications of FLC chromatin that include dimethylation of histone H3 at Lys9 (H3K9) and Lys27 (H3K27). Here, we report that A. thaliana LIKE Heterochromatin Protein 1 (LHP1) is necessary to maintain the epigenetically repressed state of FLC upon return to warm conditions typical of spring. LHP1 is enriched at FLC chromatin after prolonged exposure to cold, and LHP1 activity is needed to maintain the increased levels of H3K9 dimethylation at FLC chromatin that are characteristic of the vernalized state.
Prim B Singh - One of the best experts on this subject based on the ideXlab platform.
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mutations in the Heterochromatin Protein 1 hp1 hinge domain affect hp1 Protein interactions and chromosomal distribution
Chromosoma, 2005Co-Authors: Ramakrishna Badugu, Prim B Singh, Youngdong Yoo, Rebecca KellumAbstract:Heterochromatin Protein 1 (HP1) is a conserved component of the highly compact chromatin found at centromeres and telomeres. A conserved feature of the Protein is multiple phosphorylation. Hyper-phosphorylation of HP1 accompanies the assembly of cytologically distinct Heterochromatin during early embryogenesis. Hypo-phosphorylated HP1 is associated with the DNA-binding activities of the origin recognition complex (ORC) and an HMG-like HP1/ORC-Associated Protein (HOAP). Perturbations in HP1 localization in pericentric and telomeric Heterochromatin in mutants for Drosophila ORC2 and HOAP, respectively, indicate roles for these HP1 phosphoisoforms in Heterochromatin assembly also. To elucidate the roles of hypo- and hyper-phosphophorylated HP1 in Heterochromatin assembly, we have mutated consensus Protein Kinase-A phosphorylation sites in the HP1 hinge domain and examined the mutant Proteins for distinct in vitro and in vivo activities. Mutations designed to mimic hyper-phosphorylation render the Protein incapable of binding HOAP and the DmORC1 subunit but confer enhanced homo-dimerization and lysine 9-methylated histone H3-binding to the Protein. Mutations rendering the Protein unphosphorylatable, by contrast, do not affect homo-dimerization or binding to lysine 9-di-methylated histone H3, HOAP, or DmORC1 but do confer novel DmORC2-binding activity to the Protein. This mutant Protein is ectopically localized throughout the chromosomes when overexpressed in vivo in the presence of a full dose of DmORC2. This ectopic targeting is accompanied by ectopic targeting of lysine 9 tri-methylated histone H3. The distinct activities of these mutant Proteins could reflect distinct roles for HP1 phosphoisoforms in Heterochromatin structure and function.
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components of a pathway maintaining histone modification and Heterochromatin Protein 1 binding at the pericentric Heterochromatin in mammalian cells
Journal of Biological Chemistry, 2004Co-Authors: Huawei Xin, Prim B Singh, Hoguen Yoon, Jiemin Wong, Jun QinAbstract:Heterochromatin is a higher order chromatin structure that is important for transcriptional silencing, chromosome segregation, and genome stability. The establishment and maintenance of Heterochromatin is regulated not only by genetic elements but also by epigenetic elements that include histone tail modification (e.g. acetylation and methylation) and DNA methylation. Here we show that the p33ING1-Sin3-HDAC complex as well as DNA methyltransferase 1 (DNMT1) and DNMT1-associated Protein 1 (DMAP1) are components of a pathway required for maintaining proper histone modification and Heterochromatin Protein 1 binding at the pericentric Heterochromatin. p33ING1 and DMAP1 interact physically and co-localize to Heterochromatin in the late S phase, and both are required for Heterochromatin Protein 1 binding to Heterochromatin. Although the p33ING1-Sin3-HDAC and DMAP1-DNMT1 complexes are recruited independently to pericentric Heterochromatin regions, they are both required for deacetylation of histones and methylation of histone H3 at lysine 9. These data support a cooperative model for histone deacetylation, methylation, and DNA methylation in maintaining pericentric Heterochromatin structure throughout cell divisions.
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the ki 67 Protein interacts with members of the Heterochromatin Protein 1 hp1 family a potential role in the regulation of higher order chromatin structure
The Journal of Pathology, 2002Co-Authors: Thomas Scholzen, Ian G Cowell, Elmar Endl, Claudia Wohlenberg, Sjaak Van Der Sar, Johannes Gerdes, Prim B SinghAbstract:The expression of the nuclear Protein Ki-67 (pKi-67) is strictly correlated with cell proliferation. Because of this, anti-Ki-67 antibodies can be used as operational markers to estimate the growth fraction of human neoplasia in situ. For a variety of tumours, the assessment of pKi-67 expression has repeatedly been proven to be of prognostic value for survival and tumour recurrence, but no cellular function has yet been ascribed to the Ki-67 Protein. This study shows that a C-terminal domain of pKi-67 (Kon21) is able to bind to all three members of the mammalian Heterochromatin Protein 1 (HP1) family in vitro and in vivo. This interaction can be manipulated in living cells, as evidenced by ectopic expression of GFP-tagged HP1 Proteins in HeLa cells, which results in a dramatic relocalization of endogenous pKi-67. Taken together, the data presented in this study suggest a role for pKi-67 in the control of higher-order chromatin structure. Copyright © 2001 John Wiley & Sons, Ltd.
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histones h3 h4 form a tight complex with the inner nuclear membrane Protein lbr and Heterochromatin Protein 1
EMBO Reports, 2001Co-Authors: Hara Polioudaki, Prim B Singh, Niki Kourmouli, Victoria Drosou, Alexandra Bakou, Panayiotis A Theodoropoulos, Thomas Giannakouros, Spyros D GeorgatosAbstract:We have recently shown that Heterochromatin Protein 1 (HP1) interacts with the nuclear envelope in an acetylation-dependent manner. Using purified components and in vitro assays, we now demonstrate that HP1 forms a quaternary complex with the inner nuclear membrane Protein LBR and a sub-set of core histones. This complex involves histone H3/H4 oligomers, which mediate binding of LBR to HP1 and cross-link these two Proteins that do not interact directly with each other. Consistent with previous observations, HP1 and LBR binding to core histones is strongly inhibited when H3/H4 are modified by recombinant CREB-binding Protein, revealing a new mechanism for anchoring domains of under-acetylated chromatin to the inner nuclear membrane.
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binding of Heterochromatin Protein 1 to the nuclear envelope is regulated by a soluble form of tubulin
Journal of Biological Chemistry, 2001Co-Authors: Niki Kourmouli, Prim B Singh, George Dialynas, Spyros D Georgatos, Chrysoula Petraki, Athina Pyrpasopoulou, Panayiotis A TheodoropoulosAbstract:We have previously shown that the mouse Heterochromatin Protein 1 homologue M31 interacts dynamically with the nuclear envelope. Using quantitative in vitro assays, we now demonstrate that this interaction is potently inhibited by soluble factors present in mitotic and interphase cytosol. As indicated by depletion and order-of-addition experiments, the inhibitory activity co-isolates with a 55-kDa Protein, which binds avidly to the nuclear envelope and presumably blocks M31-binding sites. Purification of this Protein and microsequencing of tryptic peptides identify it as alpha2/6:beta2-tubulin. Consistent with this observation, bona fide tubulin, isolated from rat brain and maintained in a nonpolymerized state, abolishes binding of M31 to the nuclear envelope and aborts M31-mediated nuclear envelope reassembly in an in vitro system. These observations provide a new example of "moonlighting," a process whereby multimeric Proteins switch function when their aggregation state or localization is altered.