A deletion mutant of L-A double-stranded RNA replicates like M1 double-stranded RNA

Abstract

X double-stranded RNA (dsRNA) is a 0.52-kilobase dsRNA molecule that arose spontaneously in a nonkiller strain of Saccharomyces cerevisiae originally containing L-A and L-BC dsRNAs (L-BC is the same size as L-A but shares no homology with it). X hybridized with L-A, and direct RNA sequencing of X showed that the first 5' 25 base pairs (of the X positive strand) and at least the last 110 base pairs of the 3' end were identical to the ends of L-A dsRNA. X showed cytoplasmic inheritance and, like M1, was dependent on L-A for its maintenance. X was encapsidated in viruslike particles whose major coat protein was provided by L-A (as is true for M1), and X was found in viruslike particles with one to eight X molecules per particle. This finding confirms our "head-full replication" model originally proposed for Ml and M2. Like M1 or M2, X lowers the copy number of L-A, especially in a ski host. Surprisingly, X requires many chromosomal MAK genes that are necessary for M1 but not for L-A.

Presence of non-supressive, M2-related dsRNAs molecules in Saccharomyces cerevisiae strains isolated from spontaneous fermentations

“…This result con¢rmed that NS dsRNA was encapsidated in viral particles and not merely a naked dsRNA like T or W dsRNAs [20]. The next step was to investigate whether NS was a deletion fragment derived from either L (similar to X dsRNA [21]) or M2 dsRNA (as in S forms derived from M1 dsRNA [4,10]), or if this component was a new dsRNA species not related to those described above. This aspect was elucidated by performing Northern blot hybridization experiments.…”

Viruses of Fungi and Protozoans: Is Everyone Sick?

“…That is, if a viral dsRNA is small enough and its transcript is not extruded from a particle after transcription, ensuing replication of the transcript will result in a particle with two molecules of the same dsRNA. This process may continue until multiple copies of very small dsRNAs are present in some particles (Esteban and Wickner, 1988).…”

“…There are chromosomal genes (MAK) required for M1 and S maintenance, but usually not for L1 maintenance (Wickner, 1986(Wickner, , 1989. At least some of these are also necessary for an L1 DI mutant (Esteban and Wickner, 1988). The viral binding site (VBS), internal replication enhancer (IRE) (Esteban et al, 1989), and interference sequence (INS) (Huan et al, 1991;Shen and Bruenn, 1993) are probably synonymous, and consist of a 19-31-bp sequence with defined primary and secondary structure (Shen and Bruenn, 1993;Yao et al, , 1997.…”

The frenemies within: viruses, retrotransposons and plasmids that naturally infectSaccharomycesyeasts

“…To persist within Saccharomyces yeasts, they package and replicate their genomic dsRNAs (500-3000 base pairs) by sequestering proteins encoded by totiviruses (Bostian et al, 1980). Some satellite viruses appear not to encode any proteins, only RNA sequences that enable their encapsidation and replication (Esteban and Wickner, 1988). However, other satellite viruses can encode proteinaceous antifungal 'killer' toxins that are translated, post-translationally processed and excreted by yeasts (Schmitt and Breinig, 2006).…”