Figure 8. Loss of Ras1-GTP hydrolysis prevents coordination of actin polymerization following pheromone stimulation.

A, Cells transformed with Pob1 (pPob1) were treated with pheromone and imaged following staining with calcofluor white. Values shown are percentage loss of cell viability. B, Pheromone-dependent reporter gene activity was quantified using the sxa2>lacZ reporter construct in strains expressing pPob1. Pob1 expression enabled an increased transcriptional response in strains lacking gap1. All values mean of triplicate determinations (±S.E.M). C, Rhodamine-phalloidin staining of actin wild type and strains containing indicated mutations. All mitotically growing cells (0 μM pheromone) display polarized actin at the cell tips (asterix). Following treatment with 10 μM pheromone elongating wild type cells exhibit defined actin patches (asterix) and cables (arrows). All mutant strains failed to coordinate actin polymerization and a single growth site was not defined. These defects were restored upon increased expression of pCdc42 or pPob1. Scale bar 10 μm.