GENETIC-CONTROL OF BUD SITE SELECTION IN YEAST BY A SET OF GENE-PRODUCTS THAT CONSTITUTE A MORPHOGENETIC PATHWAY

Yeast cells choose bud sites on their surface in two distinct spatial patterns: axial for a and alpha-cells and bipolar for a/alpha-cells. We have identified four genes, BUD1-BUD4, necessary for the axial pattern by isolating mutants of alpha-cells that do not exhibit this pattern. Mutations in BUD1 (which is the same as the previously identified gene RSR1) or BUD2 lead to a random budding pattern in all cell types; mutations in BUD3 or BUD4 lead to a bipolar pattern in all cell types. These observations indicate the existence of a basal budding pattern, requiring no BUD products, that is random; BUD1 and BUD2 act on this basal pattern to create the bipolar pattern; the further action of BUD3 and BUD4 leads to the axial pattern. These studies thus identify a set of gene products that directs cell morphogenesis to a genetically programmed site.