Fig. 7
From: Microtubule minus-end aster organization is driven by processive HSET-tubulin clusters
Proposed model for MT aster formation by HSET. a HSET’s N-terminal tail domain is able to bind either soluble (non-MT) tubulin or MT polymer (brown), whereas HSET’s C-terminal motor domain is only able to bind MT polymer (blue). The relative availability of soluble tubulin toggles HSET’s activity between the following states: b HSET is unbound to soluble (non-MT) tubulin and exists as a dimer. This motor is: (i) nonprocessive on single MTs, and (ii) provides MT–MT sliding forces within bundles of MTs similar to established models for Ncd. c HSET is bound to soluble (non-MT) tubulin and exists in heterogeneous multimotor HSET-tubulin clusters. The precise molecular and geometrical nature of these clusters remain to be determined. These motors: (i) move processively toward the minus ends of single MTs, and (ii) processively transport MTs or MT bundles along existing MT tracks to form MT asters. This ability to toggle between modes relies on the unique ability of the N-terminal tail domain to bind both soluble (non-MT) tubulin and MT polymer
