The terminal tail region of a yeast myosin-V mediates its attachment to vacuole membranes and sites of polarized growth

The Saccharomyces cerevisiae myosin-V, Myo2p, has been implicated in the polarized movement of several organelles and is essential for yeast viability. We have shown previously that Myo2p is required for the movement of a portion of the lysosome (vacuole) into the bud and consequently for proper inheritance of this organelle during cell division. Class V myosins have a globular carboxyl terminal tail domain that is proposed to mediate localization of the myosin, possibly through interaction with organelle-specific receptors. Here we describe a myo2 allele whose phenotypes support this hypothesis. vac15-1/myo2-2 has a single mutation in this globular tail domain, causing defects in vacuole movement and inheritance. Although a portion of wild-type Myo2p fractionates with the vacuole, the myo2-2 gene product does not. In addition, the mutant protein does not concentrate at sites of active growth, the predominant location of wild-type Myo2p. Although deletion of the tail domain is lethal, the myo2-2 gene product retains the essential functions of Myo2p. Moreover, myo2-2 does not cause the growth defects and lethal genetic interactions seen in myo2-66, a mutant defective in the actin-binding domain. These observations suggest that the myo2-2 mutation specifically disrupts interactions with selected myosin receptors, namely those on the vacuole membrane and those at sites of polarized growth.