FIGURE 3:

The cell fusion defect in cdc42-138 is not due to defective pheromone signaling. (A) cdc42-138 has no defect in signaling in the context of STE20-ΔCRIB. STE20Δ−CRIB (MY10925; black bars) and STE20-ΔCRIB cdc42-138 (MY10926; gray bars), transformed with fus1-LacZ (pSB231), were treated with the indicated concentrations of α-factor for 90 min and their response measured via β-galactosidase assay. Error bars represent SD of three independent experiments. (B–D) cdc42-138 still exhibits a cell fusion defect in the STE20-ΔCRIB background. (B) STE20-ΔCRIB (MY10925) and STE20-ΔCRIB cdc42-138 (MY10926) were mated to fus2 (MY10797) for 4 h at 30°C, and diploids were selected by replica plating to selective media (C, D) Cytoplasmic transfer assays were performed using the same strains as in B, in which one partner expresses cytoplasmic GFP. (C) Examples of zygotes showing transfer (top) or in which cell fusion was blocked (bottom). The latter phenotype corresponds to the “Full” Fus⁻ cell fusion defect. (D) Quantification of the data in C. More than 460 zygotes were imaged in two independent experiments. (E) The defect in cdc42-138 is not mating-type specific. WT and cdc42-138 cells were mated in the orientations indicated. Gray bars, partial Fus⁻ zygotes; black bars, full Fus⁻ zygotes. n ≥ 176 zygotes imaged in two independent experiments.