title: 20S RNA narnavirus defies the antiviral activity of SKI1/XRN1 in Saccharomyces cerevisiae.
abstract: 20S RNA virus is a persistent positive strand RNA virus found in Saccharomyces cerevisiae. We previously observed that the virus generated in vivo from a launching vector possessed the correct RNA termini without extra sequences. Here we present evidence that the SKI1/XRN1 5'-exonuclease plays a major role in the elimination of the non-viral upstream sequences from the primary transcripts. The virus, once generated, however, is fairly unaffected by overexpression or deletion of SKI1/XRN1. By contrast, the copy number of the L-A double-stranded RNA virus in the same host is greatly increased by the deletion of SKI1/XRN1, and overexpression of the gene cured L-A virus from the cells at a high frequency. 20S RNA virus, unlike L-A virus, has a strong secondary structure at its 5'-end: the first four nucleotides are G, and they are buried at the bottom of a long stem structure, features known to inhibit the SKI1/XRN1 5'-exonuclease progression. Mutations that weakened the 5'-stem structure made 20S RNA virus vulnerable to SKI1/XRN1. These results, together with the data on L-A virus, indicate a strong anti-RNA virus activity of SKI1/XRN1. Given that 20S RNA virus resides and replicates in the cytoplasm without a protective capsid, our results suggest that the strong secondary structure at the 5'-end is crucial for the 20S RNA virus to evade the host SKI1/XRN1 defense.
authors.affiliation: Instituto de Microbiología Bioquímica, Departamento de Microbiología y Genética, Consejo Superior de Investigaciones Científicas/Universidad de Salamanca, Salamanca 37007, Spain. mrosa@usal.es
authors.forename: Rosa
authors.initials: R
authors.lastname: Esteban
authors.forename: Lorena
authors.initials: L
authors.lastname: Vega
authors.forename: Tsutomu
authors.initials: T
authors.lastname: Fujimura
mesh_terms: D000998:Antiviral Agents / Q000494:pharmacology; D001483:Base Sequence; D002213:Capsid / Q000378:metabolism; D003593:Cytoplasm / Q000378:metabolism; D005095:Exoribonucleases / Q000502:physiology*; D017353:Gene Deletion; D015967:Gene Expression Regulation, Viral; D005800:Genes, Fungal; D008969:Molecular Sequence Data; D009154:Mutation; D009690:Nucleic Acid Conformation; D017433:Protein Structure, Secondary; D012328:RNA Viruses / Q000378:metabolism*; D012331:RNA, Fungal / Q000235:genetics; D012441:Saccharomyces cerevisiae / Q000378:metabolism* / Q000821:virology*; D029701:Saccharomyces cerevisiae Proteins / Q000502:physiology*
chemical_list: D000998:Antiviral Agents; D012331:RNA, Fungal; D029701:Saccharomyces cerevisiae Proteins; D005095:Exoribonucleases; C068398:XRN1 protein, S cerevisiae