Two distinct regions in a yeast myosin-V tail domain are required for the movement of different cargoes

The Sacchnromyces cerevisiae myosin-V, Myo2p, is essential for polarized gr owth, most likely through transport of secretory vesicles to the developing bud. Myo2p is also required for vacuole movement, a process not essential for growth. The globular region of the myosin-V COOH-terminal tail domain i s proposed to bind cargo. Through random mutagenesis of this globular tail, we isolated six new single point mutants defective in vacuole inheritance, but not polarized growth. These point mutations cluster to four amino acid s in an Il-amino acid span, suggesting that this region is important for va cuole movement. In addition, through characterization of myo2-Delta AflII, a deletion of amino acids 1,459-1,491, we identified a second region of the globular tail specifically required for polarized growth. Whereas this mut ant does not support growth, it complements the vacuole inheritance defect in myo2-2 (G1248D) cells. Moreover, overexpression of the myo2-Delta AfEII globular tail interferes with vacuole movement, but not polarized growth. T hese data indicate that this second region is dispensable for vacuole movem ent. The identification of these distinct subdomains in the cargo-binding d omain suggests how myosin-Vs can move multiple cargoes. Moreover, these stu dies suggest that the vacuole receptor for Myo2p differs from the receptor for the essential cargo.