THE DOUBLE-STRANDED-RNA GENOME OF MAIZE ROUGH DWARF FIJIVIRUS CONTAINS BOTH MONO AND DICISTRONIC SEGMENTS

An existing cDNA library of the segmented double-stranded RNA genome o f maize rough dwarf virus, a plant-infecting reovirus of the genus Fij ivirus was used to further characterise three genome segments. Segment s S7, S8 and S10 were completely sequenced and found to consist of 193 6, 1900 and 1802 base pairs, respectively. They all contained the cons erved structural motifs present in all genome segments of plant-infect ing reoviruses. Computer analysis indicated that the coding strands of segments S7 and S10 each contained a single large open reading frame [ORF], consisting of 591 and 558 codons, respectively, as is the norm for reovirus genome segments. Segment S8 contained two large non overl apping ORFs consisting of 347 and 209 codons, located in the 5' and 3' terminal domains, respectively; an arrangement already described for segment S6. In vitro translation experiments confirmed that the gene p roducts of gel-purified dsRNA genome segments S7 and S10 were single p olypeptides of 68 and 63 kDa, respectively. Transcription/translation of a plasmid carrying a full-length cDNA copy of segment S8 yielded tw o (40 and 25 kDa) polypeptides. The nucleotide sequences of segments S 7 and S10 were aligned with those of the corresponding segments of ric e black-streaked dwarf virus, another member of the genus Fijivirus, a nd found to be almost identical.