Localization and molecular function of G protein andγ-tubulin in the mitotic apparatus

海胆卵的中心体是有丝分裂器(MA)的组织中心，含有一个相对分子质量为51,000(P51)的G蛋白，它是微管组装过程中细胞核的组成部分。这种蛋白质成分包含在微管组织颗粒(MTOG)中。另一方面，研究表明，γ-微管蛋白和RAN-GTP结合蛋白定位于中心体，在微管形核中发挥作用。然后，从未受精和受精的海胆卵中制备MTOG组分，并通过Western blotting分析γ-微管蛋白的定位。然而，我们未能在MTOG组分中检测到γ-微管蛋白。当然，我们从MTOG部分证实了p51的强烈信号。MTOG组分吸附在乳胶珠表面，形成星形微管组装。与乳胶珠结合的蛋白质组分不含γ-微管蛋白。抗p51抗体强烈抑制胶乳微珠启动的抗原肽形成，而抗γ-微管蛋白抗体对其抑制作用较弱。因此，γ-微管蛋白在海胆卵中不起作用的可能性是存在的，尽管不排除细胞在MA形成中具有启动微管的多余机制的可能性。

The centrosomes of sea urchin egg function as an organizing center of the mitotic apparatus (MA), containing a G protein of MW 51,000 (p51) which serves as a component of the nucleus in microtubule assembly. This protein component is contained in the microtubule-organizing granules (MTOG). On the the hand, it has been shown that γ-tubulin and Ran- GTP binding protein are localized to the centrosome, playing a role in microtubule nucleation. Then, MTOG fraction was prepared from both unfertilized and fertilize sea urchin eggs and localization or γ-tubulin was analized by Western blotting. However, we failed to detect γ-tubulin in the MTOG fraction. We, of course, confirmed a strong signal of p51 from the MTOG fraction. The MTOG fraction was adsorbed on the surface of Latex beads, forming astral-shaped microtubule assembly. The protein components bound to the Latex beads did not contain γ-tubulin. The aster formation initiated from the Latex beads was strongly inhibited by anti-p51 antibodies but slightly by anti-γ-tubulin aantibodies. Therefore, there is a possiblility that γ-tubulin does not work in sea urchin egg, although the possibility that cells possess redundant machinery for initiation of microtubule in MA formation would not be excluded.