Resolution improvement of X-ray diffraction data of crystals of a vesicular stomatitis virus nucleocapsid protein oligomer complexed with RNA.

Vesicular stomatitis virus (VSV) is a non-segmented negative-stranded RNA virus. The nucleocapsid (N) protein of VSV is found tightly associated with the viral genomic RNA and this complex serves as the template for transcription and replication. A method for the soluble expression of the N protein in Escherichia coli has previously been reported. An N protein-RNA oligomer was isolated from this system, the stoichiometry of which was determined to be ten molecules of the N protein bound to approximately 90 nucleotides of RNA. Here, the crystallization of this protein-nucleic acid complex is presented. The crystals belong to space group P2(1)2(1)2, with unit-cell parameters a = 165.65, b = 235.35, c = 75.71 A and a diffraction limit of 6 A. Self-rotation function analysis has shown the oligomer to have tenfold rotational symmetry. In a search to identify heavy-atom derivatives, uranyl acetate was discovered to stabilize the crystals, giving them an increase in diffraction limits to beyond 2.9 A. Based on the internal symmetry of the oligomer, the size of the oligomer determined previously by negative-stained electron microscopy, the space-group symmetry and packing considerations, the packing arrangement in the crystal has been determined.