FIG. 1.

Isolation of Ste7^S368P activators. (A) Model for the yeast pheromone-stimulated MAPK pathway. The pheromone-stimulated MAPK pathway induces transcription of mating-specific genes such as FUS1. The FUS1p-HIS3 reporter gene consists of the FUS1 upstream activation sequence joined to the HIS3 open reading frame. This reporter allows signal activity in a his3Δ FUS1p-HIS3 strain to be monitored by its ability to grow on medium lacking exogenous histidine (His phenotype). A his3Δ ste11Δ FUS1p-HIS3 STE7^S368P strain has a His⁻ phenotype because the activity of Ste7^S368P is still dependent on the presence of the upstream Ste11 MAPKKK (17). Presence of Ste7^S368P activators (shown as X) in this strain should confer a His⁺ phenotype. (B) Suppression of ste11Δ STE7^S368P by BCK1 or PKH2. Strain SY1984-P (his3Δ ste11Δ FUS1p-HIS3 STE7^P368; top) (45) or SY1984 (his3Δ ste11Δ FUS1p-HIS3 STE7; bottom) (40) was transformed with the indicated plasmids, and each transformant was streaked onto SC-His plates and incubated at 30°C. Plasmids were YEplac195 (vector), YCp-STE11 (STE11), YEp-BCK1 (BCK1), YEp-PKH1 (PKH1), and YEp-PKH2 (PKH2).