title: L-A-lus, a new variant of the L-A totivirus found in wine yeasts with Klus killer toxin-encoding Mlus double-stranded RNA: possible role of killer toxin-encoding satellite RNAs in the evolution of their helper viruses.
abstract: Yeast killer viruses are widely distributed in nature. Several toxins encoded in double-stranded RNA (dsRNA) satellites of the L-A totivirus have been described, including K1, K2, K28, and Klus. The 4.6-kb L-A genome encodes the Gag major structural protein that forms a 39-nm icosahedral virion and Gag-Pol, a minor fusion protein. Gag-Pol has transcriptase and replicase activities responsible for maintenance of L-A (or its satellite RNAs). Recently we reported a new killer toxin, Klus. The L-A virus in Klus strains showed poor hybridization to known L-A probes, suggesting substantial differences in their sequences. Here we report the characterization of this new L-A variant named L-A-lus. At the nucleotide level, L-A and L-A-lus showed only 73% identity, a value that increases to 86% in the amino acid composition of Gag or Gag-Pol. Two regions in their genomes, however, the frameshifting region between Gag and Pol and the encapsidation signal, are 100% identical, implying the importance of these two cis signals in the virus life cycle. L-A-lus shows higher resistance than L-A to growth at high temperature or to in vivo expression of endo- or exonucleases. L-A-lus also has wider helper activity, being able to maintain not only Mlus but also M1 or a satellite RNA of L-A called X. In a screening of 31 wine strains, we found that none of them had L-A; they carried either L-A-lus or a different L-A variant in K2 strains. Our data show that distinct M killer viruses are specifically associated with L-As with different nucleotide compositions, suggesting coevolution.
authors.affiliation: Instituto de Biología Funcional y Genómica, Consejo Superior de Investigaciones Científicas/Universidad de Salamanca, Salamanca, Spain.
authors.forename: Nieves
authors.initials: N
authors.lastname: Rodríguez-Cousiño
authors.forename: Pilar
authors.initials: P
authors.lastname: Gómez
authors.forename: Rosa
authors.initials: R
authors.lastname: Esteban
mesh_terms: D000595:Amino Acid Sequence; D001483:Base Sequence; D019143:Evolution, Molecular; D006378:Helper Viruses / Q000235:genetics* / Q000378:metabolism; D055646:Killer Factors, Yeast / Q000235:genetics*; D034622:RNA Interference; D012330:RNA, Double-Stranded / Q000235:genetics; D019244:RNA, Satellite; D012367:RNA, Viral / Q000235:genetics; D012441:Saccharomyces cerevisiae / Q000235:genetics / Q000378:metabolism*; D013696:Temperature; D019197:Totivirus / Q000235:genetics* / Q000378:metabolism; D014764:Viral Proteins / Q000235:genetics* / Q000378:metabolism; D014920:Wine / Q000382:microbiology
chemical_list: D055646:Killer Factors, Yeast; D012330:RNA, Double-Stranded; D019244:RNA, Satellite; D012367:RNA, Viral; D014764:Viral Proteins