Mutations in the palm region of a plus-strand RNA virus polymerase result in attenuated phenotype

Institut für Virologie (FB Veterinärmedizin), Justus-Liebig-Universität, Frankfurter Straße 107, D-35392 Giessen, Germany Correspondence Paul Becher Paul.Becher{at}vetmed.uni-giessen.de The three-dimensional structure of RNA-dependent RNA polymerases (RdRps) is highly conserved among RNA viruses. In a previous study, a unique set of mutant strains of Bovine viral diarrhea virus was obtained, encompassing either a genomic deletion of six codons or duplications of between 1 and 45 codons; these mutations affect different parts of the palm region, the most conserved part of RdRps containing the catalytic centre. In the present study, a detailed characterization of the RdRp mutant viruses was performed, demonstrating different degrees of a small-plaque phenotype in cell culture, correlating with significantly reduced viral RNA synthesis and delayed virus replication. Taken together, the results of this study demonstrate a surprising flexibility within the palm region of a plus-strand RNA virus RdRp, resulting in viral attenuation in vitro . This interesting insight into an essential viral protein may have implications for the development of vaccines and attenuated viral vectors. Supporting material and a supplementary figure showing RT-PCR analyses of total RNA derived from cell-culture passages of the RdRp mutant strains are available in JGV Online.