Evolutionary relationship of ubiquitous Saccharomyces cerevisiae dsRNA viruses

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, 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, for the first time we obtained full 5’-UTR and 3’-UTR sequences of M2 satellite. Highly conserved sequence regions along with highly variable fragments were discovered at protein level, revealing clear trend to form clusters among different L-A Gag-Pol proteins. The obtained data confirm that each L-A virus variant can specifically maintain a distinct type of satellite dsRNA; at the same time, L-A redundancy toward certain M satellite has been discovered. This work has been supported by RCL grant SIT-7/2015.