Recent experiments reconstituting microtubule plus end tracking activity coupled with structural determination of microtubule plus end domains and plus end complexes are revealing the hierarchy, regulatory features, and potential mechanisms of plus end tracking proteins. Primary plus end tracking proteins include EB1 and XMAP215, while a host of secondary, EB1-dependent plus end proteins have been identified and characterized, including CLIP-170 and SKIP-motif proteins. Single molecule in vitro reconstitution assays show that XMAP215 is a processive polymerases that drives tubulin polymerization. Analysis of the EB1-microtubule interaction indicates EB1 actively promotes A-form microtubule lattice growth and rapidly exchanges with subsecond dwell times.
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