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A more recent version of this article appeared on December 1, 2006
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Submitted on November 3, 2005
Revised on September 8, 2006
Accepted on September 25, 2006
-Tubulin Complex
Wellcome Trust Centre for Cell Biology, Edinburgh University, Edinburgh, EH9 3JR, United Kingdom
Monitoring Editor: Trisha Davis
Relatively little is known about the in vivo function of individual components of the eukaryotic
-tubulin complex (
-TuC). We identified three genes, gfh1+, mod21+ and mod22+, in a screen for fission yeast mutants affecting microtubule organization. gfh1+ is a previously characterized
-TuC protein weakly similar to human
-TuC subunit GCP4, while mod21+ is novel and shows weak similarity to human
-TuC subunit GCP5. We show that mod21p is a bona fide
-TuC protein and that, like gfh1
mutants, mod21
mutants are viable. We find that gfh1
and mod21
mutants have qualitatively normal microtubule nucleation from all types of microtubule organizing centers (MTOCs) in vivo but quantitatively reduced nucleation from interphase MTOCs, and this is exacerbated by mutations in mod22+. Simultaneous deletion of gfh1p, mod21p and alp16p, a third nonessential
-TuC protein, does not lead to additive defects, suggesting that all three proteins contribute to a single function. Coimmunoprecipitation experiments suggest that gfh1p and alp16p are codependent for association with a small "core"
-TuC, while mod21p is more peripherally associated, and that gfh1p and mod21p may form a subcomplex independent of the small
-TuC. Interestingly, sucrose gradient analysis suggests that the major form of the
-TuC in fission yeast may be a small complex. We propose that gfh1p, mod21p and alp16 act as facultative "noncore" components of the fission yeast
-TuC and enhance its microtubule-nucleating ability.
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