A unifying model for the propagation of prion proteins in yeast brings insight into the [PSI+] prion
Fig 5
The GdnHCl curing experiment and propagon counting.
(A) Two phase propagon counting experiment. Propagons are distributed in dividing cells under GdnHCl treatment. Cells are then plated onto regular medium and the color phenotype ([PSI+] or [psi−]) of each subsequent colony is determined by color assay. The number of [PSI+] colonies is counted and gives the propagon count. (B) Qualitative representation of the curves obtained during the GdnHCl curing experiment. In black is the percentage of [PSI+] cells in the colony (logarithmic scale), in red is the number of [PSI+] cells in the colony (logarithmic scale). The three phases are separated by solid vertical lines. First the number of [PSI+] cells grows as fast as the whole colony, which is growing exponentially all through the experiment. Then, [psi−] cells appear and the fraction of [PSI+] cells starts decreasing. Finally, the number of [PSI+] cells reaches a plateau but the whole colony keeps growing exponentially, hence the exponential decrease of the fraction of [PSI+] cells. See [9] for an experimental example of such curves.