Active motor proteins can couple cargo to the ends of growing microtubules

In living cells, dynamic microtubule ends interact with specialized protein complexes located on microtubule targets such as chromosomes and the cell cortex. A significant role in coupling microtubule ends to these complexes has been attributed to motor proteins, which are thought to provide a physical link while at the same time allowing for microtubule growth or shrinkage. In the past, motor-coated beads have been shown to be able to follow the ends of depolymerizing microtubules, in a direction opposite to their natural walking direction. Here we show that beads coated with plus-end-directed motors can also stay attached for several seconds to the ends of growing microtubules. Upon arrival at the microtubule end, fast-moving beads reduce their velocity to the microtubule growth velocity. We show that the tendency to stay attached depends on the initial bead velocity and that the microtubule growth velocity is unaffected by the presence of the bead.

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