Boi1 and Boi2 direct secretion of specific exocytic vesicles in budding yeast. boi1/2

Boi1 and Boi2 (Boi1/2) have been implicated in polarized growth in the budding yeast Saccharomyces cerevisiae. In addition, Boi1/2 are required for inhibition of cytokinesis in response to chromosome bridges, via the NoCut checkpoint. How Boi1/2 act in these two distinct processes is not well understood. Here, we show that Boi1/2 are essential for a late step in the fusion of specific types of vesicles with the plasma membrane. Cells lacking Boi1/2 show normal cytokinesis and secretion of invertase-containing vesicles, but accumulate Bgl2-containing vesicles and are defective in bud growth. Gain of function of the exocyst rescued Bgl2 secretion and bud growth in boi1 boi2 cells, but also restored cytokinesis in the presence of chromosome bridges. We propose that Boi1/2 mediate the sorting of specific vesicles at the plasma membrane for exocyst-dependent secretion, allowing the differential regulation of membrane fusion events during bud growth and cytokinesis.