The Saccharomyces cerevisiae
myosin-V, Myo2p, is essential for polarized growth, probably through
transport of secretory vesicles to the developing bud. Myo2p is also
required for movement of a portion of the mother cell vacuole to the
bud, a process not essential for growth. The carboxyl-terminal
globular tail of class V myosins is proposed to interact with
receptors on cargo organelles. Through random mutagenesis of this
domain, we obtained seven unique single point mutants with defects in
vacuole inheritance, but not polarized growth. One of these mutants
was myo2-2 (G1248D), the others clustered to D1297, L1301,
N1304, and N1307, amino acids located on one face of a predicted
alpha-helix. Conversely, we identified a second region of the Myo2p
tail required only for polarized growth. A deletion of amino acids
1459-1491, cannot support growth as the sole myo2 gene, but can
support vacuole inheritance in myo2-2 cells. This observation
that specific regions of the globular tail are required for different
functions of Myo2p predicts the presence of cargo-specific receptors
for Myo2p. In order to identify the vacuolar receptor for Myo2p, we
screened for both multicopy and genomic suppressors of the myo2
vacuole inheritance mutants identified above. We have found two open
reading frames that partially suppress the myo2-2 vacuole
inheritance defect when overexpressed. In addition, we have identified
one dominant suppressor mutant.
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