Identifying and characterizing novel players involved in S. cerevisiae re-orientation

Chemotropism is an important phenomenon essential for many biological processes. How cells are able to interpret an extracellular chemical gradient and locate its source has been widely studied in S. Cerevisiae, a eukaryotic model for directional sensing. In the pheromone signaling pathway, binding of pheromone to cell surface receptors initiates a signaling cascade that leads haploid cells of opposite mating types to arrest their cell cycle, form mating projections towards their nearest partner, and eventually fuse to form a diploid cell. In a normal mating mixture, these cells are exposed to very dynamic pheromone gradients and therefore they must be able to change their direction according to the changes in the gradient. Here we recovered a mutant through a directed screen that is defective in reorienting its direction of growth in response to a dynamic gradient. We show that sst2∆ cells are less able to reorient their mating projections in both the diploid formation reorientation assay (DFO) and the zygote formation reorientation assay (ZFO). Our data suggests Sst2p plays a greater role in axis reorientation than in orientation.