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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

发布:2017-09-08约字共12页下载文档
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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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