Modulation of polyglutamine toxicity by the plasmid-borne release factor genes.

<p>A - An extra copy of <i>SUP45</i> gene, located on the centromeric plasmid under endogenous promoter, ameliorates toxicity of 103Q in the <i>ubc4</i>Δ [<i>PSI⁺</i>] strain, as seen from serial decimal dilutions plated onto the galactose medium selective for both poly-Q and <i>SUP45</i> (or control) plasmids. B – Amelioration of [<i>PSI⁺</i>]-dependent polyglutamine toxicity by a plasmid-borne extra copy of <i>SUP45</i> gene is detected for both endogenous (<i>CEN-SUP45</i>) galactose-inducible (<i>GAL-SUP45</i>) promoters, for both 103Q and 103QP constructs, and in both <i>ubc4</i>Δ and <i>UBC4⁺</i> strains. Antitoxic effect of the plasmid-borne <i>SUP45</i> gene in the <i>ubc4Δ</i> strain is comparable to antitoxic effect of <i>AQT</i>. Toxicity was scored on the galactose medium selective for both poly-Q and <i>SUP45</i> (or control) plasmids. C and D – Centromeric plasmids with <i>SUP45</i> gene under endogenous (C) or galactose-inducible <i>P_GAL</i> (D) promoters increase levels of Sup45 protein (Sup45p) both [<i>UBC4⁺</i>] and <i>ubc4</i>Δ strains. Cultures were grown in liquid -Ura -Leu glucose (C) or -Ura -Leu galactose/raffinose (D) medium. Ade2 (Ade2p) protein is shown as a loading control. E and F – Plasmids, expressing the <i>SUP45</i> alleles with either C-terminal deletion, <i>SUP45</i>Δ<i>C19</i> (that abolishes Sup45 function and interaction with Sup35) (E) or missense mutation <i>sup45-103</i>, T62C (that impairs Sup45 function) (F) from the endogenous <i>SUP45</i> promoter, do not ameliorate 103Q and 103QP toxicity, as scored on the galactose medium selective for both plasmids.