p25 of the dynactin complex plays a dual role in cargo binding and dynactin regulation

, it is dispensable for dynein-dynactin to interact with ΔC-HookA (cytosolic HookA lacking its early endosome-binding C terminus) and is not critical for dynein-mediated early endosome transport. Using mutagenesis, imaging, and biochemical approaches, we found that several p25 regions are required for the ΔC-HookA-dynein-dynactin interaction, with the N terminus and loop1 being the most critical regions. Interestingly, p25 was also important for the microtubule (MT) plus-end accumulation of dynactin. This p25 function in dynactin localization also involved p25's N terminus and the loop1 critical for the ΔC-HookA-dynein-dynactin interaction. Given that dynactin's MT plus-end localization does not require HookA and that the kinesin-1-dependent plus-end accumulation of dynactin is unnecessary for the ΔC-HookA-dynein-dynactin interaction, our results indicate that p25 plays a dual role in cargo binding and dynactin regulation. As cargo adapters are implicated in dynein activation via binding to dynactin's pointed end to switch the conformation of p150, a major dynactin component, our results suggest p25 as a critical pointed-end protein involved in this process.