Adaptive braking by Ase1 prevents overlapping microtubules from sliding completely apart.

Overlapping antiparallel microtubules are important in cellular structures such as the mitotic spindle. Diez and colleagues use an in vitro system and mathematical modelling to show that the formation of stable overlaps involves a motor such as kinesin-14, which slides microtubules apart, and a passive microtubule crosslinker, Ase1, which accumulates at microtubule overlapping regions and slows microtubule sliding to prevent their separation.