Required for establishment of the axial budding pattern in yeast cells. May be involved in the selection of future sites of septation in hyphal cells. Contributes to morphogenesis and is important for induction of hyphal growth. Also plays a role in epithelial adherence, and is involved in intestinal colonization and systemic infection. The role in adhesion is probably minor compared with its role in morphogenesis. Localizes to a ring at the mother-bud neck of yeast and pseudohyphal cells. Localizes to single or double rings distal to the junction of the mother cell and germ tube in hyphal cells. Requires septins for proper localization. Also found at the cell-surface of blastospores. Belongs to the BUD4 family.