Regulation of nucleolar chromatin by B23/nucleophosmin jointly depends upon its RNA binding activity and transcription factor UBF

Mol Cell Biol. 2010 Oct;30(20):4952-64. doi: 10.1128/MCB.00299-10. Epub 2010 Aug 16.

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

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Base Sequence
  • Binding Sites / genetics
  • CDC2 Protein Kinase
  • Cell Cycle
  • Cell Line
  • Cell Nucleolus / genetics
  • Cell Nucleolus / metabolism*
  • Chromatin / genetics
  • Chromatin / metabolism*
  • Cyclin B / genetics
  • Cyclin B / metabolism
  • Cyclin-Dependent Kinases
  • DNA Primers / genetics
  • HeLa Cells
  • Humans
  • Mitosis / genetics
  • Mitosis / physiology
  • Molecular Chaperones / antagonists & inhibitors
  • Molecular Chaperones / genetics
  • Molecular Chaperones / metabolism
  • Mutant Proteins / genetics
  • Mutant Proteins / metabolism
  • Mutation
  • Nuclear Proteins / antagonists & inhibitors
  • Nuclear Proteins / genetics
  • Nuclear Proteins / metabolism*
  • Nucleophosmin
  • Phosphorylation
  • Pol1 Transcription Initiation Complex Proteins / genetics
  • Pol1 Transcription Initiation Complex Proteins / metabolism*
  • RNA / genetics
  • RNA / metabolism*
  • RNA, Ribosomal / genetics
  • RNA, Ribosomal / metabolism
  • RNA, Small Interfering / genetics
  • Recombinant Proteins / genetics
  • Recombinant Proteins / metabolism
  • Transcription, Genetic

Substances

  • Chromatin
  • Cyclin B
  • DNA Primers
  • Molecular Chaperones
  • Mutant Proteins
  • NPM1 protein, human
  • Nuclear Proteins
  • Pol1 Transcription Initiation Complex Proteins
  • RNA, Ribosomal
  • RNA, Small Interfering
  • Recombinant Proteins
  • transcription factor UBF
  • Nucleophosmin
  • RNA
  • CDC2 Protein Kinase
  • CDK1 protein, human
  • Cyclin-Dependent Kinases