X-RAY STRUCTURE OF CARNATION MOTTLEVIRUS AT 3.2 Å RESOLUTION A. M.Mikhailov, E. Yu. Morgunova, B. K. Vainshtein, Institute of Crystallography, Moscow, Russia, D.I.Stuart, E.E.Fry, Oxford University, Oxford OX1 3QU, UK, Z.Dauter, K.S.Wilson, EMBL Outstation, DESY, Hamburg, Germany

The structure of the Carnation Mottle Virus (CMtV) capsid protein has been determined at 3.2 Å resolution by the method of molecular replacement. The virion consists of the protein shell, a molecule of genome RNA and two short non-genome RNA fragments. The capsid is composed of 180 copies of the same protein with molecular weight of 37,787 Da arranged in accordance with T=3 icosahedral symmetry. X-ray data (140,483 unique reflections; R(I)merge=8.2%; completeness=91%, sp.gr. I23; a=382.6 Å; z=2) were collected only from 4 crystals using the synchrotron radiation with an image plate as detector. The coordinates of TBSV were used as a searching model at 6 Å resolution. Refinement has been performed using XPLOR with 5-fold non-crystallographic symmetry constraints. An R-factor of 18.3% (r.m.s. deviation from ideality for bond distances are 0.021 Å and for angles are 4.15deg.) in the resolution range 6.0-3.2 Å (using 140,248 unique reflections) for the final model of CMtV, containing 7,479 independent non-hydrogen atoms, three calcium ions and three sulphate ions. No water molecules are included in the model. The structural and biochemical results lead us to consideran alternative assembly pathway.