title: The location of calcium ions in southern bean mosaic virus.
abstract: X-ray diffraction data were collected from crystalline southern bean mosaic virus soaked in EDTA at pH 5.5. Under these conditions, the virus does not swell, although much of the Ca2+ and Mg2+ is removed from the virions. A difference electron density map, at 5.0-A resolution, between this and the native data showed three independent peaks per icosahedral asymmetric unit. One was located on the quasi-threefold axis at a site where a cation would be liganded to three quasi-related glutamates. The other two were located on the protein-RNA interface related by the quasi-threefold axis, thus leaving the other related site vacant. Atomic absorption spectroscopy results suggest that these sites are all occupied by calcium ions.
authors.affiliation: Department of Biological Sciences, Purdue University, West Lafayette, Indiana 47907, USA.
authors.forename: S S
authors.initials: SS
authors.lastname: Abdel-Meguid
authors.forename: T
authors.initials: T
authors.lastname: Yamane
authors.forename: K
authors.initials: K
authors.lastname: Fukuyama
authors.forename: M G
authors.initials: MG
authors.lastname: Rossmann