%0 Journal Article
%T Tetrameric Structure of Centromeric Nucleosomes in Interphase Drosophila Cells
%A Yamini Dalal
%A Hongda Wang
%A Stuart Lindsay
%A Steven Henikoff
%J PLOS Biology
%D 2012
%I Public Library of Science (PLoS)
%R 10.1371/journal.pbio.0050218
%X 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 ˇ°beads-on-a-stringˇ± 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.
%U http://www.plosbiology.org/article/info%3Adoi%2F10.1371%2Fjournal.pbio.0050218