Expression of individual members of the Ssa family in yeast and effects on [ PSI+] phenotype. Each member of the Ssa family was expressed as the sole source of Ssa in the yeast strain G402 by plasmid shuffle technique. Cells were streaked from 5-FOA onto YPD and following 3 days incubation at 30°C colonies were diluted in water and 20 μl spots were placed on -ade plates and incubated at 30°C for 3 days. Colour of the mutant strains ranged from white to pink, reflecting the varying degree of ade 2–1 suppression due to the mutation. The extent of ade 2–1 suppression is also reflected as density of growth on -ade plates. [psi-] variants were produced by curing [PSI+] by streaking on 3 mM Gdn-HCl.