A low-resolution structure of rice dwarf virus determined by ab initio phasing.

Rice dwarf virus crystals belong to space group I222 with cell parameters a = 770 (2), b = 795 (5), c = 814 (5) A and alpha = beta = gamma = 90 degrees. The unit cell of the crystal contains two viruses at the origin and body-centred positions. Using data synthesized from a rice dwarf virus model crystal in the space group I222, the possibility of ab initio phasing was thoroughly examined. The centric nature of the initial phases was unexpectedly broken by extensive iteration of the non-crystallographic symmetry averaging. The structure of rice dwarf virus was then solved with ab initio phasing up to 20 A resolution. The triangulation number determined by the present study is T = 13, which is different from the triangulation number, T = 9, previously determined by electron microscopy [Uyeda & Shikata (1982). Ann. Phytopathol. Soc. Jpn, 48, 295-300].