Figure 2.

Elimination of the [PSI⁺] determinant by GuHCl requires cell division. Two identical cultures of the [PSI⁺] strain BSC783/4a were grown at 30°C in YEPD supplemented with 3 mM GuHCl. One culture was maintained in exponential growth (●), while the other was allowed to enter stationary phase (○), after 10 hr (approximately four generations) of exponential growth. The [PSI⁺] fraction of the cultures were determined, as a function of time, on the basis of the red/white colony ratio of culture aliquots, grown on solid ¼YEPD medium. Each data point represents an average of three culture samples. The dashed line represents the best fit to a simple segregational model, with variables pre-existing prion seeds and generation time (as described in Materials and Methods).