The C. elegans UNC-84 protein is a nuclear envelope protein that is involved in nuclear anchoring and migration during development. The S. pombe Sad1 protein localizes at the spindle pole body. UNC-84 and and Sad1 share a common C-terminal region, that is often termed the SUN (Sad1 and UNC) domain. In mammals, the SUN domain is present in two proteins, Sun1 and Sun2. The SUN domain of Sun2 has been demonstrated to be in the periplasm.