Golgi membranes (yellow) move after encountering microtubule-bound GFP-p150Glued.

Vaughan et al., reporting on page 305, have used live-cell imaging to characterize the dynamic interactions of dynactin with growing microtubule plus-ends. The results provide substantial new insights into the regulation of these interactions, and suggest a new model for organelle transport and anchoring.

Previous work identified the p150Glued subunit of dynactin as a specific binding partner for cytoplasmic dynein. To characterize this protein further, the authors tracked GFP-tagged p150Glued using time-lapse imaging. P150Glued associated with growing microtubule plus-ends to form “comet tails,” which reflect binding followed by delayed release. The delay suggests that p150Glued binding to the growing plus-ends may be followed by multiple molecular events at the microtubule tip, including the phosphorylation of p150Glued that mediates its release.

Contact of p150Glued comet tails with Golgi-derived membranes was correlated with the initiation of transport of these membranes. Vaughan et al. propose that growing microtubules probe the cytoplasm for organelles in need of transport. Dynactin on the organelles captures the microtubules, and also recruits motor proteins through its specific interaction with cytoplasmic dynein. A similar search-and-capture model has been proposed for kinetochore–microtubule interactions, potentially revealing a universal mechanism for microtubule-based transport. ▪