CAMSAPs and nucleation-promoting factors control microtubule release from γ-TuRC

gamma-Tubulin ring complex (gamma-TuRC) is the major microtubule-nucleating factor. After nucleation, microtubules can be released from gamma-TuRC and stabilized by other proteins, such as CAMSAPs, but the biochemical cross-talk between minus-end regulation pathways is poorly understood. Here we reconstituted this process in vitro using purified components. We found that all CAMSAPs could bind to the minus ends of gamma-TuRC-attached microtubules. CAMSAP2 and CAMSAP3, which decorate and stabilize growing minus ends but not the minus-end tracking protein CAMSAP1, induced microtubule release from gamma-TuRC. CDK5RAP2, a gamma-TuRC-interactor, and CLASP2, a regulator of microtubule growth, strongly stimulated gamma-TuRC-dependent microtubule nucleation, but only CDK5RAP2 suppressed CAMSAP binding to gamma-TuRC-anchored minus ends and their release. CDK5RAP2 also improved selectivity of gamma-tubulin-containing complexes for 13- rather than 14-protofilament microtubules in microtubule-capping assays. Knockout and overexpression experiments in cells showed that CDK5RAP2 inhibits the formation of CAMSAP2-bound microtubules detached from the microtubule-organizing centre. We conclude that CAMSAPs can release newly nucleated microtubules from gamma-TuRC, whereas nucleation-promoting factors can differentially regulate this process. Rai et al. report that CAMSAPs can bind to minus ends of microtubules attached to gamma-tubulin ring complex (gamma-TuRC) and drive microtubule release. They show that CDK5RAP2, but not CLASP2, inhibits CAMSAP-mediated microtubule release from gamma-TuRC.