Evidence for a branched pathway in the polarized cell division of Saccharomyces cerevisiae

Cells of Saccharomyces cerevisiae can choose a bud site in one of two different spatial patterns (axial or bipolar) determined by their mating type. Genes important for bud-site selection have been identified and a linear model describing the hierarchy of these genes was proposed. We have uncovered a new class of genes which is required only for the bipolar pattern. The phenotype of the corresponding mutants coupled with epistasis experiments with some budding mutants already described suggest the existence of specific genes for the bipolar pathway.