Motor-binding component of the dynactin complex which assists cytoplasmic dynein by increasing its processivity and by regulation of its cargo binding (By similarity). The dynactin complex is required for the spindle translocation late in anaphase and is involved in a cell wall synthesis checkpoint. Component of the dynactin complex composed of at least ARP1, JNM1, NIP100 and ARP10. Dynactin comprises a short rod of the ARP1 filament attached to ARP10 at its pointed-end and probably associated with the capping protein at its barbed-end. The rod is implicated in dynein cargo binding. A sidearm formed by NIP100 projects from the ARP1 filament and is implicated in motor binding (By similarity). Localizes to spindle poles throughout the cell cycle. Present with 238 molecules/cell in log phase SD medium.