Purified dsRNAs from multiple viruses and satellites isolated from Saccharomyces yeasts. Saccharomyces cerevisiae

A large-scale screen to determine the diversity of double-stranded RNA (dsRNA) viruses in the model yeast Saccharomyces cerevisiae identified novel viruses from the family Partitiviridae. Most S. cerevisiae partitiviruses (ScPVs) were found associated with strains of yeasts isolated from coffee and cacao beans. The existence of partitiviruses was confirmed by sequencing the viral dsRNAs and purifying and visualizing isometric, non-enveloped viral particles. ScPVs have a typical bipartite genome encoding an RNA-dependent RNA polymerase (RdRP) gene and a coat protein (CP) gene. Phylogenetic analysis of ScPVs identified three species of ScPV, which are most closely related to viruses of the genus Cryspovirus from the mammalian pathogenic protozoan Cryptosporidium parvum. Molecular modeling of the ScPV RdRP revealed a conserved tertiary structure and catalytic site organization compared to the RdRPs of the Picornaviridae. The ScPV CP is the smallest identified in the Partitiviridae and has structural homology to those of other partitiviruses. ScPV CP appears to lack a protrusion domain that is a conspicuous feature of other partitivirus particles. It is possible to transfer ScPVs to laboratory strains of S. cerevisiae, which provides future opportunities to study partitivirus-host interactions using the powerful genetic tools available in this model organism.