Figure 4. Sc_Hsp104 does not propagate or cure the S. cerevisiae [PSI⁺] prion.

(A) Sp_Hsp104 cannot sustain [PSI ⁺] propagation. A [PSI ⁺] ΔSc_hsp104 strain complemented by a plasmidic Sc_HSP104 gene (YJW532) was transformed with an empty vector or with a plasmid expressing Sp_hsp104⁺ under the control of the endogenous Sc_HSP104 promoter. After shuffling of the Sc_HSP104-encoding plasmid, cells were streaked on YPD¼ to test the maintenance of [PSI ⁺]. Control strains show the expected white color of [PSI ⁺] cells (Ψ-74-D694) and the red color of [psi ⁻] cells (74-D694). (B) Overexpression of Sp_Hsp104 does not cure [PSI ⁺]. A [PSI ⁺] strain (Ψ-74-D694) was transformed with an empty vector or with plasmids overexpressing (↑) either Sc_HSP104 or Sp_hsp104⁺ under the control of the GAL1 promoter. Cells were streaked on YPD¼ to assess the appearance of red colonies, which indicates the curing of [PSI ⁺]. [PSI ⁺] (Ψ-74-D694) and [psi ⁻] (74-D694) strains are shown as color controls.