Arf3p GTPase is a key regulator of Bud2p activation for invasive growth in Saccharomyces cerevisiae

The regulation and signaling pathways involved in the invasive growth of yeast have been studied extensively because of their general applicability to fungal pathogenesis. Bud2p, which functions as a GTPase-activating protein (GAP) for Bud1p/Rsr1p, is required for appropriate budding patterns and filamentous growth. The regulatory mechanisms leading to Bud2p activation, however, are poorly understood. In this study, we report that ADP-ribosylation factor 3p (Arf3p) acts as a regulator of Bud2p activation during invasive growth. Arf3p binds directly to the N-terminal region of Bud2p and promotes its GAP activity both in vitro and in vivo. Genetic analysis shows that deletion of BUD1 suppresses the defect of invasive growth in arf3Δ or bud2Δ cells. Lack of Arf3p, like that of Bud2p, causes the intracellular accumulation of Bud1p-GTP. The Arf3p–Bud2p interaction is important for invasive growth and facilitates the Bud2p–Bud1p association in vivo. Finally, we show that under glucose depletion–induced invasion conditions in yeast, more Arf3p is activated to the GTP-bound state, and the activation is independent of Arf3p guanine nucleotide-exchange factor Yel1p. Thus we demonstrate that a novel spatial activation of Arf3p plays a role in regulating Bud2p activation during glucose depletion–induced invasive growth.