The Rab6 GTPase Regulates Recruitment of the Dynactin Complex to Golgi Membranes

Dynactin is a multisubunit protein complex required for the activity of dynein in diverse intracellular motility processes, including membrane transport [1-3]. Dynactin can bind to vesicles and liposomes containing acidic phospholipids [4], but general properties such as this are unlikely to explain the regulated recruitment of dynactin to specific sites on organelle membranes [5]. Additional factors must therefore exist to control this process. Candidates for these factors are the Rab GTPases, which function in the tethering of vesicles to their target organelle prior to membrane fusion [6]. In particular, Rab27a tethers melanosomes to the actin cytoskeleton [7-9]. Other Rabs have been implicated in microtubule-dependent organelle motility; Rab7 controls lysosomal transport, and Rab6 is involved in microtubule-dependent transport pathways through the Golgi and from endosomes to the Golgi [10-16]. We demonstrate that dynactin binds to Rab6 and shows a Rab6-dependent recruitment to Golgi membranes. Other Golgi Rabs do not bind to dynactin and are unable to support its recruitment to membranes. Rab6 therefore functions as a specificity or tethering factor controlling the recruitment of dynactin to membranes.