Figure 4.

Ste11p is regulated by both Ste50p and Ste5p through their respective interactions with its SAM domain-containing region and the EE region. (A) The ste50Δ and the deletion of Ste50p binding domain of Ste11p had the same effect on the pheromone-induced cell cycle arrest. Yeast strain YCW340 (MATa ssk2Δ ssk22Δ ste11Δ) (left) and YCW555 (MATa ssk2Δ ssk22Δ ste11Δ ste50Δ) (right) were transformed with plasmids indicated or the cloning vector and examined for α-factor–induced growth inhibition by halo assays (MATERIALS AND METHODS). Approximately 1 × 10⁶ exponentially growing cells were embedded in 5 ml melted agar and spread on prewarmed plates, and 5 μg of α-factor in 50% methanol were spotted on each plate. The halos were scored after 24 h incubation at 30°C. (B) The ste50Δ and the deletion of the Ste50p binding domain of Ste11p had the same effect on the pheromone-induced FUS1 expression. Strains used in A were cotransformed with plasmid pSB234 (FUS1::LacZ::URA3). Exponentially growing cells were treated with 3 μM of α-factor, and samples were taken at the time intervals indicated. β-galactosidase activity was assayed as described in MATERIALS AND METHODS and expressed in Miller units. Data represent the mean of two to three independent experiments.