Abstract
Histone chaperones regulate the density of incorporated histone proteins around DNA transcription sites and therefore constitute an important site-specific regulatory mechanism for the control of gene expression. At present, the targeting mechanism conferring this site specificity is unknown. We previously reported that the histone chaperone B23/nucleophosmin associates with rRNA chromatin (r-chromatin) to stimulate rRNA transcription. Here, we report on the mechanism for site-specific targeting of B23 to the r-chromatin. We observed that, during mitosis, B23 was released from chromatin upon inactivation of its RNA binding activity by cdc2 kinase-mediated phosphorylation. The phosphorylation status of B23 was also shown to strongly affect its chromatin binding activity. We further found that r-chromatin binding of B23 was a necessary condition for B23 histone chaperone activity in vivo. In addition, we found that depletion of upstream binding factor (UBF; an rRNA transcription factor) decreased the chromatin binding affinity of B23, which in turn led to an increase in histone density at the r-chromatin. These two major strands of evidence suggest a novel cell cycle-dependent mechanism for the site-specific regulation of histone density via joint RNA- and transcription factor-mediated recruitment of histone chaperones to specific chromosome loci.
Publication types
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Research Support, Non-U.S. Gov't
MeSH terms
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Base Sequence
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Binding Sites / genetics
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CDC2 Protein Kinase
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Cell Cycle
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Cell Line
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Cell Nucleolus / genetics
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Cell Nucleolus / metabolism*
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Chromatin / genetics
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Chromatin / metabolism*
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Cyclin B / genetics
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Cyclin B / metabolism
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Cyclin-Dependent Kinases
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DNA Primers / genetics
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HeLa Cells
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Humans
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Mitosis / genetics
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Mitosis / physiology
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Molecular Chaperones / antagonists & inhibitors
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Molecular Chaperones / genetics
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Molecular Chaperones / metabolism
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Mutant Proteins / genetics
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Mutant Proteins / metabolism
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Mutation
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Nuclear Proteins / antagonists & inhibitors
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Nuclear Proteins / genetics
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Nuclear Proteins / metabolism*
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Nucleophosmin
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Phosphorylation
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Pol1 Transcription Initiation Complex Proteins / genetics
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Pol1 Transcription Initiation Complex Proteins / metabolism*
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RNA / genetics
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RNA / metabolism*
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RNA, Ribosomal / genetics
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RNA, Ribosomal / metabolism
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RNA, Small Interfering / genetics
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Recombinant Proteins / genetics
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Recombinant Proteins / metabolism
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Transcription, Genetic
Substances
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Chromatin
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Cyclin B
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DNA Primers
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Molecular Chaperones
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Mutant Proteins
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NPM1 protein, human
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Nuclear Proteins
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Pol1 Transcription Initiation Complex Proteins
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RNA, Ribosomal
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RNA, Small Interfering
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Recombinant Proteins
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transcription factor UBF
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Nucleophosmin
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RNA
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CDC2 Protein Kinase
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CDK1 protein, human
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Cyclin-Dependent Kinases