ste2^7XR confers a defect in GFP-Gβ tracking. (A–C) Representative time-lapse images. MATa cells expressing in situ–tagged GFP-Gβ were mixed with an equal number of MATα cells and imaged from cytokinesis to fusion. The fluorescent images show the localization of GFP-Gβ as the MATa cells orient toward their mating partners (dashed purple circles). The blue arrowheads indicate the leading edge of the tracking crescent before morphogenesis. The yellow arrowheads indicate the final position of the GFP-Gβ peak and eventual site of fusion. (A) GFP-Gβ tracking in a WT MATa cell. (B and C) GFP-Gβ tracking in MATa ste2^7XR cells. Examples of ste2^7XR cells in which the tracking GFP-Gβ crescent overshot the presumptive CS before centering and intensifying at the eventual fusion site (B; 40%); failed to reach the presumptive CS, resulting in an angled zygote (C; 25%). Incidence of abnormal GFP-Gβ tracking in WT versus ste2^7XR cells: P < 0.0001 (χ²); n = 20.