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© The Rockefeller University Press, 0021-9525/1997//1041 $5.00
The Journal of Cell Biology, Volume 138, Number 5, , 1997 1041-1053

Article

Mitotic Spindle Positioning in Saccharomyces cerevisiae Is Accomplished by Antagonistically Acting Microtubule Motor Proteins



Frank R. Cottingham and M. Andrew Hoyt

Department of Biology, The Johns Hopkins University, Baltimore, Maryland 21218

Proper positioning of the mitotic spindle is often essential for cell division and differentiation processes. The asymmetric cell division characteristic of budding yeast, Saccharomyces cerevisiae, requires that the spindle be positioned at the mother–bud neck and oriented along the mother–bud axis. The single dynein motor encoded by the S. cerevisiae genome performs an important but nonessential spindle-positioning role. We demonstrate that kinesin-related Kip3p makes a major contribution to spindle positioning in the absence of dynein. The elimination of Kip3p function in dyn1{Delta} cells severely compromised spindle movement to the mother–bud neck. In dyn1{Delta} cells that had completed positioning, elimination of Kip3p function caused spindles to mislocalize to distal positions in mother cell bodies. We also demonstrate that the spindle-positioning defects exhibited by dyn1 kip3 cells are caused, to a large extent, by the actions of kinesin- related Kip2p. Microtubules in kip2{Delta} cells were shorter and more sensitive to benomyl than wild-type, in contrast to the longer and benomyl-resistant microtubules found in dyn1{Delta} and kip3{Delta} cells. Most significantly, the deletion of KIP2 greatly suppressed the spindle localization defect and slow growth exhibited by dyn1 kip3 cells. Likewise, induced expression of KIP2 caused spindles to mislocalize in cells deficient for dynein and Kip3p. Our findings indicate that Kip2p participates in normal spindle positioning but antagonizes a positioning mechanism acting in dyn1 kip3 cells. The observation that deletion of KIP2 could also suppress the inviability of dyn1{Delta} kar3{Delta} cells suggests that kinesin-related Kar3p also contributes to spindle positioning.

Abbreviations used in this paper: 5-FOA, 5-fluoro-orotic acid; DAPI, 4,6-diamidino-2-phenylindole; KRP, kinesin-related protein.

Address all correspondence to M. Andrew Hoyt, Department of Biology, The Johns Hopkins University, Baltimore, MD 21218. Tel.: (410) 516-7299. Fax: (410) 516-5213. E-mail: hoyt{at}jhu.edu

These experiments were supported by National Institutes of Health grant GM40714 awarded to M.A. Hoyt.


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