THE NUCLEOTIDE-SEQUENCE AND GENOMIC ORGANIZATION OF GRAPEVINE VIRUS-B

Grapevine virus B (GVB) is a tentative member of the genus Trichovirus , The 5'-terminal region of the RNA genome of GVB comprises 5437 nucle otides and has been sequenced by the dideoxynucleotide chain terminati on method, Evidence was obtained that the RNA is capped, Two putative open reading frames (ORFs) were identified, ORF 1 coded for a 194.7 kD a polypeptide with conserved motifs of replication-related proteins of positive-strand RNA viruses (i,e, methyltransferase, helicase and RNA -dependent RNA polymerase, in that order from the N to the C terminus) , ORF 2 encoded a 20 kDa polypeptide that did not show any significant sequence homology with protein sequences from the databases, The biol ogical function of this polypeptide was not determined. Although the 2 0 kDa product was expressed as a fusion protein with glutathione S-tra nsferase in Escherichia coli and an antiserum produced, it could not b e identified in GVB-infected plant tissue extracts, The GVB genome had the same size as that of apple chlorotic leaf spot virus (ACLSV), the type species of the genus Trichovirus, but differed substantially in the number (five compared to three), size and order of genes, Differen ces existed also in the extent of sequence homology between polymerase s, which did not cluster together in tentative phylogenetic trees, The results of this study show that definitive and tentative trichovirus species differ molecularly to an extent that may warrant a taxonomic r evision of the genus.