title: The middle region of an HP1-binding protein, HP1-BP74, associates with linker DNA at the entry/exit site of nucleosomal DNA.
abstract: In higher eukaryotic cells, DNA molecules are present as chromatin fibers, complexes of DNA with various types of proteins; chromatin fibers are highly condensed in metaphase chromosomes during mitosis. Although the formation of the metaphase chromosome structure is essential for the equal segregation of replicated chromosomal DNA into the daughter cells, the mechanism involved in the organization of metaphase chromosomes is poorly understood. To identify proteins involved in the formation and/or maintenance of metaphase chromosomes, we examined proteins that dissociated from isolated human metaphase chromosomes by 0.4 m NaCl treatment; this treatment led to significant chromosome decondensation, but the structure retained the core histones. One of the proteins identified, HP1-BP74 (heterochromatin protein 1-binding protein 74), composed of 553 amino acid residues, was further characterized. HP1-BP74 middle region (BP74Md), composed of 178 amino acid residues (Lys(97)-Lys(274)), formed a chromatosome-like structure with reconstituted mononucleosomes and protected the linker DNA from micrococcal nuclease digestion by approximately 25 bp. The solution structure determined by NMR revealed that the globular domain (Met(153)-Thr(237)) located within BP74Md possesses a structure similar to that of the globular domain of linker histones, which underlies its nucleosome binding properties. Moreover, we confirmed that BP74Md and full-length HP1-BP74 directly binds to HP1 (heterochromatin protein 1) and identified the exact sites responsible for this interaction. Thus, we discovered that HP1-BP74 directly binds to HP1, and its middle region associates with linker DNA at the entry/exit site of nucleosomal DNA in vitro.
authors.affiliation: Department of Biotechnology, Graduate School of Engineering, Osaka University, Suita, Osaka 565-0871, Japan.
authors.forename: Kayoko
authors.initials: K
authors.lastname: Hayashihara
authors.forename: Susumu
authors.initials: S
authors.lastname: Uchiyama
authors.forename: Shigeru
authors.initials: S
authors.lastname: Shimamoto
authors.forename: Shouhei
authors.initials: S
authors.lastname: Kobayashi
authors.forename: Miroslav
authors.initials: M
authors.lastname: Tomschik
authors.forename: Hidekazu
authors.initials: H
authors.lastname: Wakamatsu
authors.forename: Daisuke
authors.initials: D
authors.lastname: No
authors.forename: Hiroki
authors.initials: H
authors.lastname: Sugahara
authors.forename: Naoto
authors.initials: N
authors.lastname: Hori
authors.forename: Masanori
authors.initials: M
authors.lastname: Noda
authors.forename: Tadayasu
authors.initials: T
authors.lastname: Ohkubo
authors.forename: Jordanka
authors.initials: J
authors.lastname: Zlatanova
authors.forename: Sachihiro
authors.initials: S
authors.lastname: Matsunaga
authors.forename: Kiichi
authors.initials: K
authors.lastname: Fukui
mesh_terms: D001665:Binding Sites; D000090266:Chromobox Protein Homolog 5; D002868:Chromosomal Proteins, Non-Histone / Q000378:metabolism*; D002877:Chromosomes, Human; D004247:DNA / Q000378:metabolism*; D004268:DNA-Binding Proteins / Q000737:chemistry / Q000378:metabolism*; D006801:Humans; D008677:Metaphase; D009707:Nucleosomes / Q000378:metabolism*; D011485:Protein Binding; D011487:Protein Conformation
chemical_list: D002868:Chromosomal Proteins, Non-Histone; D004268:DNA-Binding Proteins; C548039:HP1BP3 protein, human; D009707:Nucleosomes; D000090266:Chromobox Protein Homolog 5; D004247:DNA