Component of the DASH complex, a microtubule-binding subcomplex of the outer kinetochore that is essential for proper chromosome segregation. The DASH complex mediates the formation and maintenance of bipolar kinetochore-microtubule attachments by forming closed rings around spindle microtubules and establishing interactions with proteins from the central kinetochore. Mediates interaction between the DASH and sim4 complexes leading to loading of DASH onto the kinetochore. The DASH complex oligomerizes to form rings that encircle the microtubules. Interacts with sim4. Associates with the mitotic spindle and the kinetochore. Unlike the other DASH complex members, dad1 remains associated with the kinetochore throughout the cell cycle. Belongs to the DASH complex DAD1 family.