Tetrameric structure of centromeric nucleosomes in interphase Drosophila cells

PLoS Biol. 2007 Aug;5(8):e218. doi: 10.1371/journal.pbio.0050218.

Abstract

Centromeres, the specialized chromatin structures that are responsible for equal segregation of chromosomes at mitosis, are epigenetically maintained by a centromere-specific histone H3 variant (CenH3). However, the mechanistic basis for centromere maintenance is unknown. We investigated biochemical properties of CenH3 nucleosomes from Drosophila melanogaster cells. Cross-linking of CenH3 nucleosomes identifies heterotypic tetramers containing one copy of CenH3, H2A, H2B, and H4 each. Interphase CenH3 particles display a stable association of approximately 120 DNA base pairs. Purified centromeric nucleosomal arrays have typical "beads-on-a-string" appearance by electron microscopy but appear to resist condensation under physiological conditions. Atomic force microscopy reveals that native CenH3-containing nucleosomes are only half as high as canonical octameric nucleosomes are, confirming that the tetrameric structure detected by cross-linking comprises the entire interphase nucleosome particle. This demonstration of stable half-nucleosomes in vivo provides a possible basis for the instability of centromeric nucleosomes that are deposited in euchromatic regions, which might help maintain centromere identity.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Animals
  • Centromere / chemistry*
  • Centromere / metabolism
  • Chromatin / chemistry
  • Chromatin / metabolism
  • Chromosomal Proteins, Non-Histone / chemistry
  • Chromosomal Proteins, Non-Histone / metabolism
  • Drosophila Proteins / chemistry
  • Drosophila Proteins / metabolism
  • Drosophila melanogaster* / cytology
  • Drosophila melanogaster* / genetics
  • Histones / chemistry
  • Histones / metabolism
  • Interphase / physiology*
  • Molecular Weight
  • Nucleic Acid Conformation*
  • Nucleosomes / chemistry*
  • Nucleosomes / metabolism
  • Nucleosomes / ultrastructure
  • Protein Structure, Quaternary
  • Protein Subunits / chemistry*

Substances

  • Chromatin
  • Chromosomal Proteins, Non-Histone
  • Drosophila Proteins
  • Histones
  • Nucleosomes
  • Protein Subunits