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. Subunit of dynactin, a multiprotein complex associated with dynein. Interacts with ECPAS, DYNAP and MAPRE1 (By similarity). Interacts with BICD2 (PubMed:11483508, PubMed:22956769). Interacts with CEP135 (PubMed:14983524). Present at high levels in both cytoplasmic and membrane-associated forms in neonates. Levels of membrane-associated form are greatly reduced in the adult. Belongs to the dynactin subunit 2 family.