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 localises 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 [1-2]. In mammals, the SUN domain is present in two proteins, Sun1 and Sun2 [1]. The SUN domain of Sun2 has been demonstrated to be in the periplasm [2].

1: The missing (L) UNC?. Raff JW; Curr Biol 1999;9:708-710. PMID:10508607

2: Sun2 is a novel mammalian inner nuclear membrane protein. Hodzic DM, Yeater DB, Bengtsson L, Otto H, Stahl PD; J Biol Chem 2004;279:25805-25812. PMID:15082709