Assembly of the asymmetric human ?-tubulin ring complex by RUVBL1-RUVBL2 AAA ATPase.

Abstract

The microtubule nucleator ?-tubulin ring complex (?TuRC) is essential for the function of microtubule organizing centers such as the centrosome. Since its discovery over two decades ago, ?TuRC has evaded in vitro reconstitution and thus detailed structure-function studies. Here, we show that a complex of RuvB-like protein 1 (RUVBL1) and RUVBL2 "RUVBL" controls assembly and composition of ?TuRC in human cells. Likewise, RUVBL assembles ?TuRC from a minimal set of core subunits in a heterologous coexpression system. RUVBL interacts with ?TuRC subcomplexes but is not part of fully assembled ?TuRC. Purified, reconstituted ?TuRC has nucleation activity and resembles native ?TuRC as revealed by its cryo-electron microscopy (cryo-EM) structure at ~4.0-� resolution. We further use cryo-EM to identify features that determine the intricate, higher-order ?TuRC architecture. Our work finds RUVBL as an assembly factor that regulates ?TuRC in cells and allows production of recombinant ?TuRC for future in-depth mechanistic studies.