STE50P IS INVOLVED IN REGULATING FILAMENTOUS GROWTH IN THE YEAST SACCHAROMYCES-CEREVISIAE AND ASSOCIATES WITH STE11P

STE50 is required to sustain pheromone-induced signal transduction in S. cerevisiae. Here we report that Ste50p is involved in regulating ps eudohyphal development. Both of these processes are also dependent on Ste11p. Deletion of STE50 leads to defects in filamentous growth, whic h can be suppressed by overproduction of Ste11p. Overexpression of STE 11 also suppresses the mating defects of ste50 mutants. We have analys ed the physical association between Ste50p and Ste11p in extracts of c ells harvested under various conditions. A Ste11p-Ste50p complex can b e isolated from extracts of cells in which the pheromone response has been activated, as well as from normally growing cells. Formation of t he Ste50p-Ste11p complex does not require G(alpha), G(beta), Ste20p or Ste5p. Oligomerisation of Ste11p is shown to be independent of activa tion of the pheromone response pathway, and occurs in the absence of S te50p. We conclude that Ste50p is necessary for Ste11p activity in at least two differentiation programmes: mating and filamentous growth.