Core 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. ARP1 forms the backbone filament of the dynactin rod structure and serves as the scaffold for the remaining subunits. Required for proper orientation of the mitotic spindle. Self-associates to form an actin-like filament of 8-10 monomers. 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). Membrane-associated. Present with 1580 molecules/cell in log phase SD medium. Belongs to the actin family. ARP1 subfamily.