Fig. 8. Model for stabilization of branching nucleation sites and recruitment of katanin by the Msd1–Wdr8 complex.

In wild-type cells, lattice-bound Msd1 (filled green circle) recruits cytoplasmic Wdr8 (open green circle) to form a heteromeric complex, which is translocated to and associated with γTuRC (orange) on a preexisting microtubule (green line). After nucleation of a microtubule, katanin is recruited by Msd1–Wdr8 and severs the minus end of the daughter microtubule. Direct physical interactions between katanin and Msd1–Wdr8 are yet to be demonstrated. In msd1 and wdr8 cells, nucleated γTuRC is not stably tethered to the mother microtubule and is eventually dissociated in the absence of the katanin activity. The wdr8 mutation (and probably the msd1 mutation as well) is epistatic to the katanin mutation. The figure was prepared originally by the authors.