Formin inhibitor; inhibits Bnr1p-mediated actin filament nucleation but not elongation during vegetative growth; performs distinct but overlapping roles with Hof1p to control actin cable assembly and polarized secretion; spatially focuses Bni1p at mating projection tips, and with Bud6p organizes Bni1p into clusters that nucleate actin assembly during mating projection formation; bnr1 bil2 double mutants are inviable; localizes to the cytosol, secretory vesicles and sites of polarized growth