CLA2/BUD2 functions as a GTPase-activating protein (GAP) for BUD1/RSR1 and is necessary for proper bud-site selection in yeast. BUD2 has sequence similarity to the catalytic domain of RasGAPs, and stimulates the hydrolysis of BUD1-GTP to BUD1-GDP. Elimination of Bud2p activity by mutation causes a random budding pattern with no growth defect. Overproduction of Bud2p also alters the budding pattern.