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Vol. 17, Issue 6, 2789-2798, June 2006

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The Regulation of Microtubule Dynamics in Saccharomyces cerevisiae by Three Interacting Plus-End Tracking Proteins

Michael J. Wolyniak^*, Kristina Blake-Hodek, Karena Kosco, Eric Hwang, Liru You, and Tim C. Huffaker

Department of Molecular Biology and Genetics, Cornell University, Ithaca, NY 14853-2703

Submitted September 26, 2005; Revised March 13, 2006; Accepted March 14, 2006
Monitoring Editor: Kerry Bloom

Microtubule plus-end tracking proteins (+TIPs) are a diverse group of molecules that regulate microtubule dynamics and interactions of microtubules with other cellular structures. Many +TIPs have affinity for each other but the functional significance of these associations is unclear. Here we investigate the physical and functional interactions among three +TIPs in S. cerevisiae, Stu2, Bik1, and Bim1. Two-hybrid, coimmunoprecipitation, and in vitro binding assays demonstrate that they associate in all pairwise combinations, although the interaction between Stu2 and Bim1 may be indirect. Three-hybrid assays indicate that these proteins compete for binding to each other. Thus, Stu2, Bik1, and Bim1 interact physically but do not appear to be arranged in a single unique complex. We examined the functional interactions among pairs of proteins by comparing cytoplasmic and spindle microtubule dynamics in cells lacking either one or both proteins. On cytoplasmic microtubules, Stu2 and Bim1 act cooperatively to regulate dynamics in G1 but not in preanaphase, whereas Bik1 acts independently from Stu2 and Bim1. On kinetochore microtubules, Bik1 and Bim1 are redundant for regulating dynamics, whereas Stu2 acts independently from Bik1 and Bim1. These results indicate that interactions among +TIPS can play important roles in the regulation of microtubule dynamics.

The online version of this article contains supplemental material at MBC Online (http://www.molbiolcell.org).

* Department of Microbiology and Immunology, Dartmouth Medical School, Hanover, NH 03755;

The Burnham Institute, 10901 North Torrey Pines Road, La Jolla, CA 92037;

The Scripps Research Institute, 10550 North Torrey Pines Road, San Diego, CA 92037;

Memorial Sloan Kettering Cancer Center, 1275 York Avenue, Box 216, New York, NY 10021.

Address correspondence to: Tim Huffaker ( tch4{at}cornell.edu)

Abbreviations used: FRAP, fluorescence redistribution after photobleaching; +TIP, microtubule plus-end tracking protein.

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