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.
Fred Hutchinson Cancer Research Center, Seattle, Washington, United States of America.
Yamini
Y
Dalal
Hongda
H
Wang
Stuart
S
Lindsay
Steven
S
Henikoff
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