Dynactin is a processivity factor for dynein in vivo

Dynein is a motor protein responsible for microtubule-based minus-end directed trafficking in eukaryotic cells. Dynactin is a protein complex involved in mitosis, embryonic development, intracellular trafficking and anchoring microtubules at the centrosome. While dynactin is widely recognized to improve the array of cargo with which dynein can associate, there has been some dispute over whether dynactin, which binds both dynein and microtubules, improves the distance that dynein can travel processively in the act of cargo trafficking before it dissociates from its microtubule. In this study, we compare movement parameters of wild type dynein-based vesicle movements with movements in cells where expression of dynactin's microtubule binding subunit, p150glued, has been knocked down. We find that dynactin does act as a processivity factor for dynein by increasing the distance that dynein can travel smoothly in a single movement event, but does not increase dynein's velocity.