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WOS: 000358225100082 ; PubMed ID: 26139522 ; We report the discovery and characterization of a double-stranded RNA (dsRNA) mycovirus isolated from the human pathogenic fungus Aspergillus fumigatus, Aspergillus fumigatus tetramycovirus-1 (AfuTmV-1), which reveals several unique features not found previously in positive-strand RNA viruses, including the fact that it represents the first dsRNA (to our knowledge) that is not only infectious as a purified entity but also as a naked dsRNA. The AfuTmV-1 genome consists of four capped dsRNAs, the largest of which encodes an RNA-dependent RNA polymerase (RdRP) containing a unique GDNQ motif normally characteristic of negative-strand RNA viruses. The third largest dsRNA encodes an S-adenosyl methionine-dependent methyltransferase capping enzyme and the smallest dsRNA a P-A-S-rich protein that apparently coats but does not encapsidate the viral genome as visualized by atomic force microscopy. A combination of a capping enzyme with a picorna-like RdRP in the AfuTmV-1 genome is a striking case of chimerism and the first example (to our knowledge) of such a phenomenon. AfuTmV-1 appears to be intermediate between dsRNA and positive-strand ssRNA viruses, as well as between encapsidated and capsidless RNA viruses. ; Thai Government education program; Turkish Government education program; Leverhulme TrustLeverhulme Trust; Erasmus European Union Programme ; We thank Ren Zhang (Commonwealth Scientific and Industrial Research Organisation) and Matt Dickinson (University of Nottingham) for sequence data of flax rust Melampsora lini dsRNAs, and Profs. Eugene Koonin and Valerian Dolja for their advice on phylogenetic analyses. L.K. and S.O. thank the Thai and the Turkish Government education programs, respectively, for supporting their PhD programs. R.H.A.C. thanks The Leverhulme Trust for an Emeritus Fellowship award, and I.K.-L. acknowledges the support of the Erasmus European Union Programme.