Functional analysis of dsRNAs (L1, L3, L5, and M2) associated with isometric 34-nm virions of Agaricus bisporus (white button mushroom).

cDNA clones of dsRNAs associated with La France disease of Agaricus bisporus were isolated. Clones corresponding to L1 and L5 dsRNAs were sequenced. The deduced amino acid sequence of L1 dsRNA (1078 amino acids, Mr 121K) showed significant homology with RNA-dependent RNA polymerases of other dsRNA viruses. The deduced amino acid sequence of L5 dsRNA (724 amino acids, Mr 82K) showed no homology with known proteins. Amino acid sequences of tryptic digests of three virion-associated proteins were determined. The 34-nm virion-associated protein of Mr 115K was encoded by the L1 dsRNA, thus identifying this protein as the RNA-dependent RNA polymerase. The virion-associated protein of Mr 90K was encoded by the previously sequenced L3 dsRNA. A cDNA clone of the previously sequenced M2 dsRNA was expressed in Escherichia coli and antibodies raised against this protein reacted only with a protein present in the cytoplasm of diseased A. bisporus fruit bodies but not in the 34-nm virions.