Part of the dynactin complex that activates the molecular motor dynein for ultra-processive transport along microtubules. In the dynactin soulder domain, binds the ACTR1A filament and acts as a molecular ruler to determine the length (By similarity). Modulates cytoplasmic dynein binding to an organelle, and plays a role in prometaphase chromosome alignment and spindle organization during mitosis. Involved in anchoring microtubules to centrosomes. May play a role in synapse formation during brain development (By similarity).
