Together with dynein may be involved in spindle assembly and cytokinesis. Subunit of dynactin, a multiprotein complex associated with dynein. Localizes to punctate cytoplasmic structures and to the centrosome during interphase, and to kinetochores and to spindle poles throughout mitosis. Colocalizes with dynein to the cleavage furrow and to midbody of dividing cells. Ubiquitously expressed. Highly expressed in muscle and pancreas and detected at lower levels in brain. Belongs to the dynactin subunit 3 family.