Figure 8. Overexpression of SKO1 activates the pheromone response pathway.

(A) shows flow cytometry analysis of DNA content for the empty vector control strain, P_GAL1-SKO1 strain, and the sko1Δ strain with its corresponding control strain. Overproduction of SKO1 causes a strong arrest at the G1 phase (78% of P_GAL1-SKO1 cells accumulated at the G1 phase vs. 58% of control cells at the G1 phase). In contrast, there was no obvious G1 arrest in the sko1Δ strain. (B) While the sko1Δ strain exhibits a typical yeast cell morphology, cells from the P_GAL1-SKO1 strain resemble yeast cells presented with mating pheromone (shmoos). Overexpression of SKO1 in cells expressing a green-fluorescent protein-tagged version of the mating projection marker Fus1 induces Fus1-GFP localization to the tip of the projection (shown as an overlay of the GFP channel on the DIC image), consistent with SKO1 overexpression inducing shmooing. (C) SKO1 induces shmooing when overexpressed in the deletion strains fus1Δ, fus3Δ, sst2Δ, and dig2Δ, as well as in the corresponding parental strain (BY4741), but not when overexpressed in the deletion strains ste2Δ, ste4Δ, ste5Δ, ste20Δ, ste11Δ, far1Δ, and kar4Δ, indicating that the latter genes are required for SKO1-induced shmoo formation.