An RNA-dependent RNA Polymerase Associated with the Filamentous Nucleoproteins of Rice Stripe Virus

Summary Filamentous particles of rice stripe virus (RSV) were found to be associated with an RNA-dependent RNA polymerase activity. The enzyme catalysed the synthesis in vitro of single- and double-stranded RNAs corresponding in size with RNA found in RSV particles, as well as two other dsRNAs with mol. wt. of 1.0 × 106 and 0.56 × 106. The RSV polymerase activity required Mg2+, Mn2+ or Fe2+ but not Na+, K+ or NH+ 4 which were inhibitory at concentrations of more than 50 mm. The optimum pH of the polymerase was around 8.0 at the optimum temperature, 40°C. Detergent treatment of RSV particles did not enhance the polymerase activity. Purified RSV particles contained a minor polypeptide (mol. wt. 230000) as well as coat protein; the former may be the RSV polymerase. The taxonomy of RSV is discussed in relation to enveloped animal viruses with negative-stranded RNA, which also contain an RNA-dependent RNA polymerase in virus particles.