Differential contribution of Bud6p and Kar9p to microtubule capture and spindle orientation in S. cerevisiae.
In Saccharomyces cerevisiae, spindle orientation is controlled by a temporal and spatial program of microtubule (MT)-cortex interactions. This program requires Bud6p/Aip3p to direct the old pole to the bud and confine the new pole to the mother cell. Bud6p function has been linked to Kar9p, a protein guiding MTs along actin cables. Here, we show that Kar9p does not mediate Bud6p functions in spindle orientation. Based on live microscopy analysis, kar9Delta cells maintained Bud6p-dependent MT capture. Conversely, bud6Delta cells supported Kar9p-associated MT delivery to the bud. Moreover, additive phenotypes in bud6Delta kar9Delta or bud6Delta dyn1Delta mutants underscored the separate contributions of Bud6p, Kar9p, and dynein to spindle positioning. Finally, tub2C354S, a mutation decreasing MT dynamics, suppressed a kar9Delta mutation in a BUD6-dependent manner. Thus, Kar9p-independent capture at Bud6p sites can effect spindle orientation provided MT turnover is reduced. Together, these results demonstrate Bud6p function in MT capture at the cell cortex, independent of Kar9p- mediated MT delivery along actin cables.[1]References
- Differential contribution of Bud6p and Kar9p to microtubule capture and spindle orientation in S. cerevisiae. Huisman, S.M., Bales, O.A., Bertrand, M., Smeets, M.F., Reed, S.I., Segal, M. J. Cell Biol. (2004) [Pubmed]
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