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Vol. 20, Issue 13, 3003-3011, July 1, 2009

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Dynein-Driven Mitotic Spindle Positioning Restricted to Anaphase by She1p Inhibition of Dynactin Recruitment

Department of Molecular and Cell Biology, University of California, Berkeley, Berkeley, CA 94720

Submitted March 5, 2009; Revised April 10, 2009; Accepted April 22, 2009
Monitoring Editor: Kerry S. Bloom

Dynein is a minus-end–directed microtubule motor important for mitotic spindle positioning. In budding yeast, dynein activity is restricted to anaphase when the nucleus enters the bud neck, yet the nature of the underlying regulatory mechanism is not known. Here, the microtubule-associated protein She1p is identified as a novel regulator of dynein activity. In she1 cells, dynein is activated throughout the cell cycle, resulting in aberrant spindle movements that misposition the spindle. We also found that dynactin, a cofactor essential for dynein motor function, is a dynamic complex whose recruitment to astral microtubules (aMTs) increases dramatically during anaphase. Interestingly, loss of She1p eliminates the cell-cycle regulation of dynactin recruitment and permits enhanced dynactin accumulation on aMTs throughout the cell cycle. Furthermore, localization of the dynactin complex to aMTs requires dynein, suggesting that dynactin is recruited to aMTs via interaction with dynein and not the microtubule itself. Lastly, we present evidence supporting the existence of an incomplete dynactin subcomplex localized at the SPB, and a complete complex that is loaded onto aMTs from the cytoplasm. We propose that She1p restricts dynein-dependent spindle positioning to anaphase by inhibiting the association of dynein with the complete dynactin complex.

Address correspondence to: Georjana Barnes (gbarnes{at}socrates.berkeley.edu)

Abbreviations used: MT, microtubule; aMT, astral microtubule; SPB, spindle pole body; Chr III, chromosome III; td-tomato, tandem dimer tomato.