Symmetry of belladonna mottle virus: rotation function studies

Abstract

Belladonna mottle virus, a spherial plant virus belonging to the tymovirus group, was crystallized by precipitation with polyethylene glycol 6000 in sodium citrate buffer (pH 5.6). The crystals beling to rhombohedral space group R3 (a⋍300Å, α⋍60°) with one molecule in the unit cell, and diffract X-rays to 3.5° resolution. Owing to the special interaxial angel of ~60°, the lattice can also be described in terms of a pseudo-face-centred cubic cell. The face-centring vectors of the pseudo cell form the ell edges of the rhombohedral cell. The three-dimensional X-ray diffraction data on these crystals were collected using screenless oscillation photography to a resolution of 6°.37 842 independent reflections with I/σ(I)≥2.0 were measured on 51 film paris. The cell parameters were refined to a=295.4Å and α=59.86° by a post refinement procedure. A rotation function was calculated using data between 11 and 13Å resolution. The function unambiguously reveals the partile icosahedral symmetry and orientation in the unit cell. The body diagonals of the pseudo-cubic cell are nearly tetrahedral. The icosahedral particle also has a set of tetrahedrally related threefold axes. The particle orientation is such that these two sets can be made coincident by a rotation of ~180° about the rhombohedral [111] direction.