Involvement of a nonstructural protein in the RNA synthesis of brome mosaic virus

RNA-dependent RNA polymerase (RdRp) was prepared from brome mosaic virus (BMV)-infected barley by a procedure including Nonidet-P40 treatment. The enzyme proved to be highly active, specific, and almost completely template dependent without the need for nuclease treatment [ W. A. Miller, and T. C. Hall (1983) Virology 125, 236–241] or DEAE ion exchange chromatography [ K. Maekawa and I. Furusawa (1984) Ann. Phytopathol. Soc. Japan 50, 491–499]. Two C-terminal peptides P1C and P2C derived from the nonstructural BMV proteins P1 and P2, respectively, were synthesized. Antibodies raised against these peptides were able to recognize the corresponding native proteins present in RdRp preparations. Antibodies directed against P1 C were capable of completely blocking the transcription of BMV RNA in vitro. This is the first experimental evidence that a nonstructural viral protein is present in an enzyme complex involved in tricornaviral RNA synthesis.