Noncore components of the fission yeast gamma-tubulin complex.
Relatively little is known about the in vivo function of individual components of the eukaryotic gamma-tubulin complex (gamma-TuC). We identified three genes, gfh1+, mod21+, and mod22+, in a screen for fission yeast mutants affecting microtubule organization. gfh1+ is a previously characterized gamma-TuC protein weakly similar to human gamma-TuC subunit GCP4, whereas mod21+ is novel and shows weak similarity to human gamma-TuC subunit GCP5. We show that mod21p is a bona fide gamma-TuC protein and that, like gfh1Delta mutants, mod21Delta mutants are viable. We find that gfh1Delta and mod21Delta 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 gamma-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" gamma-TuC, whereas mod21p is more peripherally associated, and that gfh1p and mod21p may form a subcomplex independently of the small gamma-TuC. Interestingly, sucrose gradient analysis suggests that the major form of the gamma-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 gamma-TuC and enhance its microtubule-nucleating ability.
Anders
Andreas
A
Wellcome Trust Centre for Cell Biology, Edinburgh University, Edinburgh EH9 3JR, United Kingdom.
Lourenço
Paula C C
PC
Sawin
Kenneth E
KE
D048430:Cell Shape; D007399:Interphase; D008869:Microtubule-Associated Proteins / Q000378:metabolism; D008870:Microtubules / Q000378:metabolism; D008938:Mitosis; D009154:Mutation / Q000235:genetics; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D012568:Schizosaccharomyces / Q000166:cytology / Q000378:metabolism*; D029702:Schizosaccharomyces pombe Proteins / Q000378:metabolism*; D008941:Spindle Apparatus / Q000378:metabolism; D014404:Tubulin / Q000378:metabolism*
C473565:Alp16 protein, S pombe; C494594:Gfh1 protein, S pombe; D008869:Microtubule-Associated Proteins; D011993:Recombinant Fusion Proteins; D029702:Schizosaccharomyces pombe Proteins; D014404:Tubulin