Fig. 2.

Ectopic expression of WOR1 in white cells drives the cells to the opaque phase. (A and B) Ectopic expression of WOR1 causes white cells to resemble opaque cells in appearance. Cell dimensions were measured in differential interference contrast images (B), and populations of cells were compared based on the distribution of length/width ratios for 50 cells per strain for each condition (A). (C) Ectopic expression of WOR1 in white cells causes them to express genes characteristic of opaque cells. Quantitative RT-PCR was used to monitor transcription of the white-specific genes WH11 and EFG1 and the opaque-specific genes SAP1 and OP4. All values were normalized to PAT1, a transcript that is not regulated by white–opaque switching. (D) Ectopic expression of WOR1 in white cells renders them sensitive to the mating pheromone α-factor. This specialized property of true opaque cells is visualized by the formation of mating projections on the ends of the cells (14). Cells were treated with α-factor (10 μg/ml in DMSO) or an equivalent amount of DMSO as a control. In A and B, “ON” and “OFF” indicate the expression of the pMET3-WOR1 construct, as controlled by media conditions. For strains that lack the pMET3-WOR1 construct, media conditions are designated by “ON” or “OFF.” For experiments shown in C and D, strains were grown in media that induces pMET3-WOR1 expression. All strains are a strains.