Nucleotide sequence of seed- and pollen-transmitted double-stranded RNA, which encodes a putative RNA-dependent RNA...

The nucleotide sequence of the largest double-stranded (ds) RNA (named dsRNA1) of three species of seed- and pollen-transmitted dsRNA species detected from Japanese pear was analyzed, and one strand was found to contain a single long open reading frame (ORF) of 1434 nucleotides that encoded a putative polypeptide containing 477 amino acid residues with a molecular mass of 54.9 kDa. This polypeptide contained amino acid sequence motifs conserved in putative RNA-dependent RNA polymerases of RNA viruses. Attempts to visually identify or purify virus-like particles associated with the dsRNAs were unsuccessful. Slow sedimentation of the dsRNA fraction suggests that the dsRNAs may be unencapsidated. The concentration of dsRNAs in the host, Japanese pear, was about 16 times higher than that from a cryptic virus, radish yellow edge virus (RYEV). These results suggest that the dsRNAs were not from cryptic viruses. Partial nucleotide sequences of the two smaller dsRNAs (named dsRNAs 2 and 3) and two other dsRNAs (named dsRNAs 4 and 5) detected from only the Japanese pear cultivar (cv.) Akita Tazawa 3 Gou were analyzed, and encoded nearly the same amino acid sequence encoded by dsRNA1.