OAT BLUE DWARF MARAFIVIRUS RESEMBLES THE TYMOVIRUSES IN SEQUENCE, GENOME ORGANIZATION, AND EXPRESSION STRATEGY

The complete nucleotide sequence and genome organization of oat blue d warf marafivirus (OBDV) were determined. The 6509 nucleotide RNA genom e encodes a putative 227-kDa polyprotein (p227) with sequence motifs s imilar to the methyltransferase, papain-like protease, helicase, and p olymerase motifs present in the nonstructural proteins of other positi ve strand RNA viruses. The 3' end of the open reading frame (ORF) that encodes p227 (ORF 227) also encodes the two capsid proteins: a 24-kDa capsid protein is presumably cleaved from the p227 polyprotein, where as the 21-kDa capsid protein appears to be translated from a subgenomi c RNA (sgRNA). Encoded amino acid and nucleotide sequence comparisons, as well as the OBDV genome expression strategy, show that OBDV closel y resembles the tymoviruses. OBDV differs from the tymoviruses in its general biology, in its lack of a putative movement gene that overlaps the replication-associated genes, and in its fusion of the capsid gen e sequences to the major ORF. OBDV also possesses a 3' poly(A) tail, a s compared to the tRNA-like structures found in most tymoviral genomes . Due to the strong similarities in genome sequence and expression str ategy, OBDV, and presumably the other marafiviruses, should be conside red a member of the tymovirus lineage of the alpha-like plant viruses. (C) 1997 Academic Press.