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Elimination of the [PSI+] prion by Hsp104 overexpression is greatly reduced in cells lacking the co-chaperones Sti1p and Cpr7p. (A) Both strains, transformed with pUKC2200 were plated onto one-quarter YEPD after 24 h following addition of galactose, and colonies allowed to develop. Colonies were photographed after 3–4 days of growth at 30 °C. (B) Each of the four strains indicated were transformed with the plasmid pUKC2200. The expression of the GAL1–HSP104 gene carried on this plasmid was induced and the percentage of cells that formed pure red Ade− colonies (i.e. that were [psi−]) was estimated as described in Materials and methods. The results are the average of three independent experiments. (C) Western blot analysis of the levels of Hsp104 in each of the four strains engineered to overexpress the HSP104 gene. For each of the four strains, samples were taken after 0, 2, 7 and 14 generations of growth. The membranes were simultaneously probed with an anti-Hsp104 and an anti-PGK antibody, the latter acting as a loading control