Genome organization of a partitivirus from the filamentous ascomycete Atkinsonella hypoxylon.

We have identified viruses in several isolates of the filamentous ascomycete Atkinsonella hypoxylon. The virus from one isolate of the fungus, 2H, was selected for genomic characterization. Purified virus particles contained three dsRNAs with sizes estimated by gel electrophoresis to be 2.2, 2.1 and 1.8 kb. A library of cDNA clones representing the three dsRNA segments of isolate 2H was synthesized, mapped and sequenced. The three segments had no significant similarity to each other, as determined by Northern blot analysis, and had sizes of 2180, 2135 and 1790 nt as determined by nucleotide sequence analysis. Long open reading frames were deduced from the sequences of dsRNAs 1 (molecular mass 78 kDa) and 2 (74 kDa), but not from dsRNA 3. Both terminal regions of dsRNA 1 and dsRNA had similar nucleotide sequences, as determined from 5' RACE clones. Comparisons of the amino acid sequence deduced from dsRNA 1 revealed similarities with viral RNA-dependent RNA polymerases. Translation in vitro of full-length cDNA clones representing dsRNAs 1 and 2 each yielded single major products of > 70 kDa by analysis on polyacrylamide gels. Based on properties of its dsRNA segments, the virus of A. hypoxylon strain 2H fits into the Partitiviridae family, and represents the first member of this family from a fungal host completely characterized at the level of primary nucleotide sequence.