CLOSE SIMILARITY BETWEEN GENOME STRUCTURES OF RICE BLACK-STREAKED DWARF AND MAIZE ROUGH DWARF VIRUSES

The complete nucleotide sequences of rice black-streaked dwarf virus (RBSDV) genome segments 8 (S8) and 7 (S7) were determined, and were found to have high sequence identities to the corresponding maize rough dwarf virus (MRDV) genome segments. RBSDV S8 and S7 consisted of 1927 and 2193 nucleotides, respectively. RBSDV S8 had a single long open reading frame (ORF) encoding 591 amino acids. RBSDV S7 had two non-overlapping ORFs encoding 362 (ORF1) and 309 (ORF2) amino acids. The two ORFs of RBSDV S7 were inserted separately into an Escherichia coli expression vector (pKK223-3). When they were expressed in E. coli cells, the products of both ORFs migrated identically at an apparent M(r) of 40K. High nucleotide sequence identity was observed between RBSDV S7 and MRDV S6 (85 %), and between the terminal regions of RBSDV S8 and MRDV S7. In addition, RBSDV S7 and MRDV S6 showed 91 % (ORF1 product) and 85 % (ORF2 product) amino acid sequence identities.