Budding yeast uses actin and a myosin, Myo2p, to accomplish polarized secretion. The simplest model for this process, which Schott et al. confirm on page 791, is based on transport: the Myo2p head walks along actin to growth sites, with vesicle cargoes attached to its tail. The alternative is a capture model. In this scenario, the Myo2p tail targets the protein to the growth site, where it can organize and polarize actin.
The transport model was in doubt because the original myo2tsmutant had severe cytoskeletal disorganization, suggesting an indirect effect on polarity. In more recent experiments, a tail region alone localized to polarized sites, but Schott et al. show that this occurs by transport. It requires a vesicle targeting factor and normal Myo2p, which presumably carries the extra tails attached to vesicle cargoes.
Schott et al....
