Localization of Bud2p, a GTPase-activating protein necessary for programming cell polarity in yeast to the presumptive bud site

Yeast cells of different cell type exhibit distinct budding patterns that r eflect the organization of the actin cytoskeleton. Bud1p (Rsr1p), a Ras-lik e GTPase, and Bud2p, a GTPase-activating protein for Bud1p, are essential f or proper budding pattern. We show that Bud2p is localized at the presumpti ve bud site in G(1) cells in all cell types and that this localization is i ndependent of Bud1p. Bud2p subsequently localizes to the mother-bud neck af ter bud emergence; this localization depends on the integrity of the septin s. These observations indicate that Bud2p becomes positioned in G(1) cells by recognizing cell type-specific landmarks at the presumptive bud site.