Extensive conservation of prokaryotic ribosomal binding sites in known and novel picobirnaviruses

Currently, the Leviviridae and Cystoviridae are the only two recognized families of prokaryotic RNA viruses. Picobirnaviruses, which are bisegmented double-stranded RNA viruses commonly found in animal stool samples, are currently thought to be animal viruses, but have not been propagated in cell culture or in an animal model. We hypothesize that picobirnaviruses are prokaryotic RNA viruses. We identified and analyzed the genomes of 38 novel picobirnaviruses and determined that a classical bacterial sequence motif, the ribosomal binding site (RBS), is present in the 5′ untranslated regions (5′ UTRs) of all of the novel as well as all previously published picobirnavirus sequences. Among all viruses, enrichment of the RBS motif is only observed in viral families that infect prokaryotes and not in eukaryotic infecting viral families. These results will enable future studies to more accurately understand the biology of picobirnaviruses.