These data clearly establish that Sti1p plays a role in the elimination of the [PSI+] prion when Hsp104 is overexpressed, but is not necessary for the continued propagation of [PSI+] when Hsp104 is present at physiological levels. Furthermore, the Cpr7p co-chaperone also plays a role in [PSI+] elimination, since the sti1Δ cpr7Δ double mutant showed an even greater resistance to [PSI+] elimination than was observed for the single knock-out strains, although the kinetic analysis suggested that its absence delayed rather than prevented the appearance of [PSI+] cells (Figure 3B).