ELUCIDATING HOW THE GAMMA-TUBULIN RING COMPLEX (γ-TuRC) NUCLEATES MICROTUBULES

Abstract

Microtubules (MTs) are dynamic cylindrical polymers made of α/β-tubulin dimers that function in many diverse and essential cellular processes such as cell division, intracellular transport, and organelle positioning. Because of their importance, it is imperative that microtubules are nucleated at the correct time and place. A protein known to be essential for MT nucleation is γ-tubulin, which together with other proteins in the cell, forms a ring-like template called the γ-tubulin ring complex (γ-TuRC). Despite its importance, little is known about how the γ-TuRC nucleates MTs. For many years, it has been proposed that the γ-TuRC undergoes a large structural change upon activation, though this has not been observed directly. In this dissertation, I present two complementary structures of the γ-TuRC. The first structure is a cryo-electron microscopy (cryo-EM) structure of the γ-TuRC with an activating protein domain, which shows dynamic movement within the complex. While theorized for many years, I present the first example of structural changes that occur to change the diameter of the γ-TuRC. The second structure is the first cryo-electron tomography (cryo-ET) sub-tomogram average of the γ-TuRC in a post-nucleation state. This reconstruction of the γ-TuRC bound to a MT provides insight into the position of the γ-TuRC in relation to a newly formed MT. Together, my work helps to further our understanding of how the universal MT nucleator, the γ-TuRC, functions to regulate the production of MTs.