Bem1 contributes to symmetry breaking by boosting the GEF activity of Cdc24. (A) Polarization of GFP-Cdc42 in axl2Δ rax1Δ BEM1 cells, axl2Δ rax1Δ bem1Δ cells, axl2Δ rax1Δ bem1^K480E,S547P cells, and axl2Δ rax1Δ bem1^K480E,S547P cells expressing CDC24^ΔPB1 from the CDC24 promoter. Experimental procedure was as described in Fig. 1 B. The plots show means from averaging three experiments, and error bars correspond to SEMs. More than 80 cells were counted per time point per experiment. (B) Maximum projections of representative cells from A. (C) Localization of Cdc24^ΔPB1-GFP in bem1^K480E,S547P cells with polarized mCherry-Cdc42 after pheromone arrest release in LatA. Z-stack images of representative cells were subjected to a 1 × 1 Gaussian filter before maximum projection. (D) Polarization of Cdc24^ΔPB1-GFP and mCherry-Cdc42 in bem1^K480E,S547P cells in LatA, quantified as in Fig. 1 K for n = 15 cells. Error bars show SEMs. Bars, 5 µm.