tetrameric structure of centromeric nucleosomes in interphase drosophila cells四聚物的着丝粒在相间果蝇细胞中核小体的结构.pdf
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PLoS BIOLOGY
Tetrameric Structure of Centromeric
Nucleosomes in Interphase Drosophila Cells
1,2 3 3 1,2*
Yamini Dalal , Hongda Wang , Stuart Lindsay , Steven Henikoff
1 Fred Hutchinson Cancer Research Center, Seattle, Washington, United States of America, 2 Howard Hughes Medical Institute, Seattle, Washington, United States of
America, 3 Biodesign Institute, Arizona State University, Tempe, Arizona, United States of America
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.
Citation: Dalal Y, Wang H, Lindsay S, Henikoff S (2007) Tetrameric structure of centromeric
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