The sequences of cDNA clones encoding most of the NI b protein, the coat protein and the 3' untranslated region of papaya ringspot virus (PRV) strains W and P have been determined. The open reading frame of P strain PRV was confirmed by amino acid analysis. Nucleotide sequence comparisons of these strains show that they share a 98-2% identity in their NI b gene regions and a 97-7% identity in their coat protein genes. The sequences of these two strains are distinct from other potyvirus types, confirming their classification as two strains of the same virus. The NI b amino acid sequence possesses conserved amino acids characteristic of RNA-dependent RNA polymerases.Comparison of the coat protein amino acid sequence with those of other potyviruses shows perfectly conserved amino acids which may have functional significance.

The 3'- and 5'-terminal sequences of the five large double-stranded RNA species (L-dsRNA; 4.5-6.0 X 10(6) daltons) of EP713, a hypovirulent strain of Endothia parasitica, were determined by mobility-shift and enzymatic methods. All the L-dsRNAs appeared to have identical terminal sequences. A heteropolymer sequence was found at one 3'-terminus and a poly(A) sequence of variable length at the other. It was possible to label only one 5'-terminus using polynucleotide kinase and [gamma-32P]ATP, and this was shown to be a poly(U) sequence of variable length. We propose that the dsRNAs have the following structure, where X represents a blocking group: (Formula: see text). A recombinant plasmid containing dsRNA-related sequences was constructed. Hybridization analysis using the recombinant probe indicated that the sequence homology among the L-dsRNAs extended beyond these terminal regions and was also shared by small dsRNAs (0.3-0.45 X 10(6) daltons).

SUMMARYDot blots of dsRNA from European and American hypovirulent (H) strains of the chestnut blight fungus, Endothia parasitica, were hybridized with 32p-5'-end-labelled fragments of denatured dsRNA of French, Italian and American origins. Although dsRNA from European or American strains reacted well with labelled RNA probes from strains from the same continent there was little or no cross-hybridization between RNA from strains from different continents.