NUCLEOTIDE-SEQUENCE ANALYSIS AND GENOMIC ORGANIZATION OF THE NY-RPV ISOLATE OF BARLEY YELLOW DWARF VIRUS

cDNA clones representing the ssRNA genome of the NY-RPV isolate of barley yellow dwarf luteovirus (BYDV) were sequenced and 5600 nucleotides of the genome were determined. The deduced genome organization has limited similarity to that of another BYDV isolate, Vic-PAV, but is identical to that of beet western yellows (BWYV) and potato leafroll (PLRV) luteoviruses. NY-RPV has six major positive-sense open reading frames (ORFs) and, by comparison with RNA-dependent RNA polymerase and nucleic acid helicase consensus sequence motifs, it is postulated that NY-RPV ORF2 and ORF3 encode the viral replicase, which is expressed by a translational frameshift mechanism. The region of the NY-RPV genome containing the 22K coat protein ORF, the apparently associated internal apparent VPg ORF and the ORF immediately 3'-proximal (ORF6) to the coat protein ORF are organized as reported for other luteoviruses. Evidence is presented showing that ORF6 is expressed by readthrough of the coat protein gene termination codon, and that this protein is associated with the intact virus as a 65K protein. Although NY-RPV infects graminaceous rather than dicotyledonous plants, the taxonomic relationships between BYDV isolates and other luteoviruses deduced from the genome organization and sequence data strongly suggest that NY-RPV is distinct from the PAV-like isolates of BYDV and is more closely related to BWYV and PLRV.