title: Evidence that SV40 VP1-DNA interactions contribute to the assembly of 40-nm spherical viral particles.
abstract: The simian virus 40 (SV40) particle is mainly composed of the major capsid protein termed VP1. VP1 self-assembles into virus-like particles (VLPs) of approximately 40 nm in diameter when over-expressed in bacteria or in insect cells, but purified VP1 does not form such a structure under physiological conditions, and thus, the mechanism of VP1 assembly is not well understood. Using a highly purified VP1 assembly/disassembly system in vitro, here we provide evidence that DNA is a factor that contributes to VP1 assembly into 40-nm spherical particles. At pH 5, for example, VP1 preferentially assembles into 40-nm particles in the presence of DNA, whereas VP1 assembles into tubular structures in the absence of DNA. Electron microscopic observations revealed that the concentration of DNA and its length are important for the formation of 40-nm particles. In addition, sucrose gradient sedimentation analysis and DNase I-sensitivity assays indicated that DNA of up to 2,000 bp is packaged into the 40-nm particles under the conditions examined. We propose that DNA may facilitate the formation of 40-nm spherical particles by acting as a scaffold that increases the local concentration of VP1 and/or by acting as an allosteric effector that alters the structure of VP1.
authors.affiliation: Graduate School of Bioscience and Biotechnology, Tokyo Institute of Technology, 4259 Nagatsuta-cho, Midori-ku, Yokohama, Kanagawa 226-8501, Japan.
authors.forename: Hiroko
authors.initials: H
authors.lastname: Tsukamoto
authors.forename: Masa-Aki
authors.initials: MA
authors.lastname: Kawano
authors.forename: Takamasa
authors.initials: T
authors.lastname: Inoue
authors.forename: Teruya
authors.initials: T
authors.lastname: Enomoto
authors.forename: Ryou-U
authors.initials: RU
authors.lastname: Takahashi
authors.forename: Naoki
authors.initials: N
authors.lastname: Yokoyama
authors.forename: Noriaki
authors.initials: N
authors.lastname: Yamamoto
authors.forename: Takeshi
authors.initials: T
authors.lastname: Imai
authors.forename: Kohsuke
authors.initials: K
authors.lastname: Kataoka
authors.forename: Yuki
authors.initials: Y
authors.lastname: Yamaguchi
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Handa
mesh_terms: D002118:Calcium / Q000378:metabolism; D036022:Capsid Proteins / Q000378:metabolism* / Q000648:ultrastructure; D004270:DNA, Circular / Q000378:metabolism* / Q000648:ultrastructure; D006863:Hydrogen-Ion Concentration; D008854:Microscopy, Electron; D013539:Simian virus 40 / Q000502:physiology*; D012964:Sodium / Q000378:metabolism; D013997:Time Factors; D014771:Virion / Q000502:physiology*; D019065:Virus Assembly / Q000502:physiology*
chemical_list: D036022:Capsid Proteins; D004270:DNA, Circular; C062481:VP1 protein, polyomavirus; D012964:Sodium; D002118:Calcium