Tetrameric structure of centromeric nucleosomes in interphase Drosophila cells.
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.
Dalal
Yamini
Y
Fred Hutchinson Cancer Research Center, Seattle, Washington, United States of America.
Wang
Hongda
H
Lindsay
Stuart
S
Henikoff
Steven
S
D000818:Animals; D002503:Centromere / Q000737:chemistry* / Q000378:metabolism; D002843:Chromatin / Q000737:chemistry / Q000378:metabolism; D002868:Chromosomal Proteins, Non-Histone / Q000737:chemistry / Q000378:metabolism; D029721:Drosophila Proteins / Q000737:chemistry / Q000378:metabolism; D004331:Drosophila melanogaster / Q000166:cytology / Q000235:genetics; D006657:Histones / Q000737:chemistry / Q000378:metabolism; D007399:Interphase / Q000502:physiology*; D008970:Molecular Weight; D009690:Nucleic Acid Conformation; D009707:Nucleosomes / Q000737:chemistry* / Q000378:metabolism / Q000648:ultrastructure; D020836:Protein Structure, Quaternary; D021122:Protein Subunits / Q000737:chemistry*
D002843:Chromatin; D002868:Chromosomal Proteins, Non-Histone; D029721:Drosophila Proteins; D006657:Histones; D009707:Nucleosomes; D021122:Protein Subunits