Immunostructural Evidence for the Template Mechanism of Microtubule Nucleation. T. J. Keating and G.G. Borisy Nat Cell Biol., 2(6):352-357, 2000

Two opposing models have been put forward to explain how the g-tubulin ring complex (g-TuRC) induces microtubule (MT) nucleation. The protofilament model proposes that the g-TuRC induces nucleation as a partially or completely straightened protofilament that becomes incorporated longitudinally into the wall of the nascent MT, while the template model predicts that the g-TuRC acts as a helical template that constitutes the base of the newly-formed polymer. We sought to distinguish between these two models by performing high-resolution structural and immunolocalization studies. We found that g-TuRC components localize to a narrow zone at the extreme minus end of the MT and that these ends terminate in a pointed cap. Together, these results strongly favor the template model of nucleation.

	Figure 1 (136 K) - . Light microscopic visualization of g-TuRC components at the ends of single MTs
	Figure 2 (268 K) - Ultrastructural localization of g-TuRC components at MT ends
	Figure 3 (296 K) - Distribution of g-TuRC components and comparison to predictions of the template and protofilament models of MT nucleation
	Figure 4 (156 K) - Models of the MT nucleating and capping structure
	Table 1 - Labeling of g-TuRC components at microtubule ends