RNA viruses, M satellites, chromosomal killer genes, and killer/nonkiller phenotypes in the 100-genomes S. cerevisiae strains

Abstract

We characterized previously identified RNA viruses (L-A, L-BC, 20S, and 23S), L-A-dependent M satellites (M1, M2, M28, and Mlus), and M satellite-dependent killer phenotypes in the Saccharomyces cerevisiae 100-genomes genetic resource population. L-BC was present in all strains, albeit in 2 distinct levels, L-BChi and L-BClo; the L-BC level is associated with the L-BC genotype. L-BChi, L-A, 20S, 23S, M1, M2, and Mlus (M28 was absent) were in fewer strains than the similarly inherited 2µ plasmid. Novel L-A-dependent phenotypes were identified. Ten M+ strains exhibited M satellite-dependent killing (K+) of at least 1 of the naturally M0 and cured M0 derivatives of the 100-genomes strains; in these M0 strains, sensitivities to K1+, K2+, and K28+ strains varied. Finally, to complement our M satellite-encoded killer toxin analysis, we assembled the chromosomal KHS1 and KHR1 killer genes and used naturally M0 and cured M0 derivatives of the 100-genomes strains to assess and characterize the chromosomal killer phenotypes.

Keywords: Saccharomyces cerevisiae; 100-genomes strains; RNA virus; associations; killer; phenotypes.

Fig. 1.

Representative gels (top) of strains carrying different species of the dsRNA totiviruses (L-A and L-BC) and satellites (M1, M2, and Mlus). Shown are isogenic strain pairs of native and L-A–cured strains. (Bottom) Corresponding PCRs from cDNAs of RNA derived from the indicated strains, probing for presence/absence of L-A (A), L-BC (B), or M (M1, M2, and Mlus). All samples were treated with DNase prior to gel and PCR analysis. Primers for PCR analysis LA-F4 + LA-R5 (L-A), LBC-F2 + LBC-R2 (L-BC), M1-F + M1-R (M1), M2-F + M2-R (M2), and Mlus-F2 + Mlus-R2 (Mlus).

Fig. 2.

Killer activity in M-containing strains. Isogenic strain pairs of native and L-A–cured strains were tested on lawns of M⁰ strains. Representative strains displaying a) K1, b) K2, c) Klus, and d) K28 killer activity are shown. For Klus, only 1 strain background (YJM428) showed sensitivity to the Mlus toxin. For K28, a corresponding M⁰ strain was not tested.

Fig. 3.

Phenotypic analysis of a) YJM1133 and b) YJM1419 L-A⁺ M⁺ parental as well as isogenic L-A⁺ M⁰ and L-A⁰ M⁰ derivatives. Ten-fold dilutions of isogenic strains differing only in the presence/absence of L-A and/or M were spotted on media with the indicated compounds and monitored for growth.