Beads coated with wild-type (WT) or oligomerization-deficient (OD) Dam1 complex were tracked while they coupled to assembling (left plots) and disassembling (right plots) microtubule tips under a constant force of ~2.4 pN applied in the direction of microtubule assembly. (a) Mean attachment lifetime for beads coupled to dynamic microtubule tips under constant load. (b) Speeds of microtubule tip assembly and disassembly while coupled to beads under constant force. In our assay conditions, the intrinsic rates of microtubule assembly and disassembly are ~6 nm s−1 and ~230 nm s−1, respectively9, 34. (c) Switch rates for microtubule tip state: from assembly to disassembly (catastrophe), and from disassembly to assembly (rescue). For microtubules alone, catastrophes occur at a frequency of ~10 hr−1 (9, 45), and rescues at ~2 hr−1 (34). In a-c, error bars indicate s.e.m.