Disease relevance of TUB4

• The toxicity of SPC98 overexpression was relieved by co-overexpression of TUB4 [1].

High impact information on TUB4

• In the presence of the gamma-tubulin antibody, microtubules fail to regrow into cytoplasmic arrays after depolymerization induced by nocodazole or cold [2].
• Thus in vivo gamma-tubulin is required for microtubule nucleation throughout the mammalian cell cycle [2].
• gamma-tubulin complexes: binding to the centrosome, regulation and microtubule nucleation [3].
• The results suggest that gamma-tubulin phosphorylation regulates the number and dynamics of microtubules [4].
• The astral microtubule organizing function of Nud1p is mediated by its interaction with the gamma-tubulin complex binding protein Spc72p [5].

Biological context of TUB4

• Evidence is provided for a physical and functional interaction between Tub4p, Spc98p and Spc97p: first, temperature-sensitive spc97(ts) mutants are suppressed by high gene dosage of SPC98 or TUB4 [6].
• Nucleation of microtubules is central to assembly of the mitotic spindle, which is required for each cell division. gamma-Tubulin is a universal component essential for microtubule nucleation from centrosomes [7].
• A role of Tub4p in microtubule organization is further suggested by an increase in chromosome loss in tub4-1 cells [8].
• In the November 2001 issue of Developmental Cell, Vogel et al. describe that the budding yeast gamma-tubulin, Tub4p, is phosphorylated at a conserved tyrosine in G1 phase of the cell cycle [4].
• The predicted amino acid sequence of the Tub4 protein (Tub4p) is 29-38% identical to members of the gamma-tubulin family [9].

Anatomical context of TUB4

• Study of a temperature sensitive tub4-1 allele revealed that TUB4 has essential functions in microtubule organization [8].
• Finally, we report the identification of a large 22 S Tub4p complex in yeast extract that contains multimers of Spc97p similar to gamma-tubulin ring complexes found in higher eukaryotic cells [7].
• These results suggest that different components of MTOCs act as receptors for gamma-tubulin complexes and that they are essential for the function of MTOCs [10].
• Homologues of Spc97p and Spc98p have been identified from yeast to mammalian cells and these are also part of gamma-tubulin complexes, suggesting that these related proteins may also interact with GTBPs at the centrosome [11].
• Loss of function of the gamma-tubulin gene by RNAi induces a strong polyploidization of mitotic germ cells and embryos, but does not affect meiosis and pronuclear migration [12].

Associations of TUB4 with chemical compounds

• Sucrose gradient sedimentation of the cytosolic fraction and immunoprecipitation experiments demonstrate that both gamma-tubulin and HsSpc98p are in the same complex [13].
• Alanine substitution for any one of these phosphorylated residues, in conjunction with an alanine substitution at residue Ser(36), is lethal in combination with alleles of SPC97, which encodes a component of the Tub4p complex [14].

Physical interactions of TUB4

• The spindle pole body component Spc98p interacts with the gamma-tubulin-like Tub4p of Saccharomyces cerevisiae at the sites of microtubule attachment [1].
• The spindle pole body component Spc97p interacts with the gamma-tubulin of Saccharomyces cerevisiae and functions in microtubule organization and spindle pole body duplication [6].
• Finally, the observation that SSA1 and YDJ1 interact genetically with a gamma-tubulin, TUB4, supports the idea that they play a role in the regulation of microtubule formation [15].
• We tested whether binding of the recombinant Tub4p complex to the spindle pole body docking protein Spc110p affects its nucleating activity [7].
• Here, we describe the identification of the essential SPB component Spc72p whose N-terminal domain interacts with the Tub4p complex on the cytoplasmic side of the SPB [10].

Other interactions of TUB4

• Previously, we have shown that the gamma-tubulin Tub4p and the spindle pole body component Spc98p are involved in microtubule organization by the yeast microtubule organizing centre, the spindle pole body (SPB) [6].
• Together, these studies provide evidence that Spc110p directly links the Tub4p complex to the SPB [16].
• The Tub4p complex binds Spc110p/Cmd1p via Spc98p and the K(d) for binding is 150 nM [7].
• Genes encoding gamma-tubulin (TUB4) or any subunit of casein kinase II (CKII) suppressed this growth defect, but did not suppress the growth defect of a mutant in another subunit of the Arp2/3 complex, arp2-1 [17].
• Gamma-tubulin is as ubiquitous in eukaryotes as alpha- and beta-tubulin [18].

Analytical, diagnostic and therapeutic context of TUB4

• Finally, immunoprecipitation and fractionation studies revealed complexes containing Tub4p, Spc98p and Spc97p [6].
• Immunofluorescence and nuclear staining experiments indicate that cells depleted of Tub4p contain defects in the organization of both cytoplasmic and nuclear microtubule arrays; such cells exhibit nuclear migration failure, defects in spindle formation, and/or aberrantly long cytoplasmic microtubule arrays [9].
• Indirect immunofluorescence experiments using a strain containing an epitope-tagged Tub4p indicate that Tub4p resides at the spindle pole body throughout the yeast cell cycle [9].
• Confocal microscopy revealed that this region corresponds to the lymphocyte microtubule organizing center, where paxillin colocalizes with alpha- and gamma-tubulin [19].
• We cloned the gamma-tubulin gene from Sz. japonicus by PCR using redundant sets of primers corresponding to conserved regions of known gamma-tubulins [20].

References