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Department of Biological Sciences, Stanford University, Stanford, California 94305-5020
Proper orientation of the mitotic spindle is
critical for successful cell division in budding yeast. To
investigate the mechanism of spindle orientation, we
used a green fluorescent protein (GFP)-tubulin fusion
protein to observe microtubules in living yeast cells. GFP-tubulin is incorporated into microtubules, allowing visualization of both cytoplasmic and spindle microtubules, and does not interfere with normal microtubule function. Microtubules in yeast cells exhibit
dynamic instability, although they grow and shrink
more slowly than microtubules in animal cells. The dynamic properties of yeast microtubules are modulated
during the cell cycle. The behavior of cytoplasmic microtubules revealed distinct interactions with the cell
cortex that result in associated spindle movement and
orientation. Dynein-mutant cells had defects in these
cortical interactions, resulting in misoriented spindles.
In addition, microtubule dynamics were altered in the
absence of dynein. These results indicate that microtubules and dynein interact to produce dynamic cortical
interactions, and that these interactions result in the
force driving spindle orientation.
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