PHEROMONE RESPONSE IN YEAST - ASSOCIATION OF BEM1P WITH PROTEINS OF THE MAP KINASE CASCADE AND ACTIN

Haploid cells of the yeast Saccharomyces cerevisiae respond to mating pheromones with polarized growth toward the mating partner. This morph ological response requires the function of the cell polarity establish ment protein Bem1p. Immunochemical and two-hybrid protein interaction assays revealed that Bem1p interacts with two components of the pherom one-responsive mitogen-activated protein (MAP) kinase cascade, Ste20p and Ste5p, as well as with actin. Mutants of Bem1p that are associated with defective pheromone-induced polarized morphogenesis interacted w ith Ste5p and actin but not with Ste20p. Thus, the association of Bem1 p with Ste20p and Ste5p may contribute to the conveyance of spatial in formation that regulates polarized rearrangement of the actin cytoskel eton during yeast mating.