Structural properties of double-stranded RNAs associated with biological control of chestnut blight fungus

Double-stranded RNAs (ds RNAs) are thought to be the cytoplasmic determinants responsible for the phenomenon of transmissible hypovirulence in the chestnut blight fungusEndothia parasitica [Murr.] Anderson. The three major ds RNA components associated with the North American hypovirulent strain, Grand Haven 2, were characterized with respect to molecular-hybridization specificity and RNase T1-digestion patterns. The large (L-RNA; ≈9 kilobase pairs) and middle-sized (M-RNA; ≈3.5 kilobase pairs) ds RNA components cross-hybridized under stringent conditions and exhibited indistinguishable partial and complete RNase T1 digestion patterns relative to their 5′ and 3′ termini. These results suggest that M-RNA was derived from L-RNA by an internal deletion event. The small (S-RNA; ≈1 kilobase pair) RNA was unrelated to L- and M-RNA by these criteria. However, all three ds RNA components contained RNase T1-resistant oligonucleotides at one 5′ terminus and at the corresponding 3′ terminus of the complementary strand. These RNase T1-resistant species exhibited properties consistent with stretches of poly(uridylic acid) and poly(adenylic acid), respectively. The combined results are discussed in terms of the structural organization of hypovirulence-associated ds RNA molecules and their similarities to “double-stranded” RNA molecules observed in plant and animal cells infected with single-stranded RNA viruses.