May be involved in ion homeostasis together with BTN1 or BTN2. Interacts with BTN2. Correct localization requires BTN2. Localizes to the mother cell in small budded cells and to the bud in medium and large budded cells. Transported to the bud tip by an actomyosin based process. Compartmentalization maintained by a septin mediated membrane diffusion barrier at the mother-bud neck.