Does yeast virus possess specificity towards replication of satellite virus?

Abstract

Saccharomyces cerevisiae has been a key experimental organism for the study of infectious diseases, including double-stranded RNA (dsRNA) viruses. The L-A dsRNA virus family of S. cerevisiae is widely distributed in nature. Several versions of L-A virus are described and new ones continue to be discovered. Some S. cerevisiae strains along with L-A dsRNA possess smaller dsRNAs, called M satellites. These dsRNAs encode a sole secretable protein, known as K1, K2, K28 and K-lus toxin. L-A genome encodes the Gag major structural protein and Gag-Pol fusion protein, formed by ribosomal frameshifting. Gag-Pol has transcriptase and replicase activities are necessary for maintenance of both L-A and M satellite dsRNAs. So far, it’s not known whether certain L-A virus has evolved to maintain a distinct type of satellite dsRNA or this phenomenon lacks inherent specificity. We developed universal strategy to obtain full length L-A and M dsRNA genomes from S. cerevisiae. Complete viral dsRNA genomes can now be cloned, as evidenced by L-A-28 dsRNA, analyzed and sequenced directly from any yeast strain by means of enzymatic manipulations on total or fractioned RNA content. We have identified previously undescribed L-A variant from different yeast strains specifically associated with certain type of M satellites. Moreover, we identified for the first time full 50-UTR and 30-UTR sequences of M2 satellite. Highly conserved sequence regions along with variable fragments were discovered at protein level, revealing clear trend to form clusters among different L-A Gag-Pol proteins. The obtained data suggest that each L-A virus variant can specifically maintain a distinct type of satellite dsRNA.