Part of the ACTR1A/ACTB filament around which the dynactin complex is built. The dynactin multiprotein complex activates the molecular motor dynein for ultra-processive transport along microtubules.
Subcellular locations: Cytoplasm, Cytoskeleton, Cytoplasm, Cytoskeleton, Microtubule organizing center, Centrosome, Cytoplasm, Cell cortex