Characterization of RNAs synthesized by the virion-associated transcriptase of rice dwarf virus in vitro

Sequence analysis of the rice dwarf phytoreovirus segment S3 transcript encoding for the major structural core protein of 114 kDa

The primary structure of rice dwarf phytoreovirus (RDV) genome segment S3 was determined. RDV S3 consists of 3195 nucleotides. A 14-bp segment-specific inverted repeat is located immediately adjacent to the conserved terminal sequence (5'GGCAAA---UGAU3'). A single long open reading frame encoding for 1019 amino acids with an Mr of 114,289 is also identified. In order to investigate the localization of the predicted polypeptide, we determined the amino acid sequence of the 26-kDa peptide fragment obtained from the structural core protein digested by Staphylococcus aureus V8 protease. The sequence of the fragment was found in the translational product presumed from the nucleotide sequence of RDV S3, indicating that RDV S3 encodes the major structural core protein of 114 kDa.

Nucleotide sequence of segment S9 of the rice dwarf virus genome

The complete nucleotide sequence of genome segment S9, which was reported as the ninth largest among the 12 genome segments of rice dwarf virus, was determined. The segment was 1,305 bp long and coded for a protein composed of 351 amino acids (Mr 38,930). The terminal sequences of the segment were found to consist of an imperfect 14 base pair inverted repeat located at positions 2-15 and 1289-1302, which is similar to that identified in other reoviruses.

In vitro synthesis of double-stranded RNA by carnation cryptic virus-associated RNA-dependent RNA polymerase

Partially purified carnation cryptic virus (CarCV) preparations possessed RNA-dependent RNA polymerase activity which was absent in comparable preparations from virus-free carnations. Enzyme activity was dependent upon the presence of virus particles, Mg2+, and the four ribonucleoside triphosphates, and was insensitive to inhibitors of DNA-dependent RNA polymerases. The 32P-labeled enzyme reaction products were largely dsRNAs as indicated by resistance to S1 nuclease and RNase A at high but not low ionic strength. The in vitro synthesized dsRNAs hybridized specifically with CarCV genomic dsRNAs, and the radioactive products present in the polymerase reaction mixture sedimented with the virus particles in sucrose density gradients. The data suggest that the RNA-dependent RNA polymerase associated with CarCV particles is a replicase which catalyzes the synthesis of copies of the genomic dsRNAs.

RNA-dependent RNA polymerase activity in two morphologically different white clover cryptic viruses

RNA-dependent RNA polymerase activities were detected in purified particles of white clover cryptic viruses 1 and 2. The polymerases of the two viruses had different requirements for optimum activity. Enzyme activity was dependent upon the presence of virus particles, Mg2+, and the four ribonucleoside triphosphates, and was insensitive to actinomycin D, alpha-amanitin, and rifampicin. The labeled reaction products were dsRNAs as indicated by CF 11 column chromatography and by their ionic-strength-dependent sensitivity to hydrolysis by RNase A and resistance to S1 nuclease. The dsRNAs synthesized in vitro had the same electrophoretic mobilities as the corresponding viral templates.