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J. Cell Biol.,
Volume 140, Number 4, February 23, 1998 873-883
Department of Anatomy and Cell Biology, University of Michigan Medical School, Ann Arbor, Michigan 48109-0616
Abstract. We have previously reported that a defect in
Myo2p, a myosin in budding yeast (Saccharomyces cerevisiae), can be partially corrected by overexpression of
Smy1p, which is by sequence a kinesin-related protein
(Lillie, S.H., and S.S. Brown. 1992. Nature. 356:358-
361). Such a functional link between putative actin- and
microtubule-based motors is surprising, so here we have tested the prediction that Smy1p indeed acts as a
microtubule-based motor. Unexpectedly, we found that
abolition of microtubules by nocodazole does not interfere with the ability of Smy1p to correct the mutant
Myo2p defect, nor does it interfere with the ability of
Smy1p to localize properly. In addition, other perturbations of microtubules, such as treatment with benomyl
or introduction of tubulin mutations, do not exacerbate
the Myo2p defect. Furthermore, a mutation in SMY1
strongly predicted to destroy motor activity does not
destroy Smy1p function. We have also observed a genetic interaction between SMY1 and two of the late
SEC mutations, sec2 and sec4. This indicates that
Smy1p can play a role even when Myo2p is wild type,
and that Smy1p acts at a specific step of the late secretory pathway. We conclude that Smy1p does not act as
a microtubule-based motor to localize properly or to
compensate for defective Myo2p, but that it must instead act in some novel way.
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