Figure 4 .

Cytoduction of [PSI⁺] into cured rtf1Δ rkr1Δ strains causes synthetic lethality. (A) An rtf1Δ rkr1Δ ade1-14 strain (KY2286) cured of prions by dissection on medium containing GuHCl was transformed with a URA3-marked RTF1 plasmid and made ρ⁰ by growth in ethidium bromide-containing medium. This strain served as a recipient for cytoduction with donor kar1 strains containing only [PSI⁺] (L2265) or [PIN⁺] (L2261). A dilution growth assay is shown with the recipient and cytoductants on YPD and YPG to show successful cytoduction of recipients, on SD-Ade to show transfer of [PSI⁺], and on 5-FOA to score for loss of the RTF1/URA3 plasmid. Plates were incubated at 30° for 2–6 days. (B) Cytoductants from A were transformed with a HIS3-marked pCUP1-SUP35NM-GFP or pCUP1-RNQ1-GFP plasmid, patched on selective plates containing 100 µM CuSO₄, and incubated in the dark at 30° before live-cell imaging was performed by confocal microscopy. Observations were made of at least three transformants per strain and 100 cells per transformant. Representative images are shown. No variability was seen among cells with respect to the GFP pattern.