InterPro domain: IPR045119

Sad1/UNC-84 (SUN)-domain proteins are inner nuclear membrane (INM) proteins that are part of bridging complexes linking cytoskeletal elements with the nucleoskeleton. Originally identified based on an ~150-amino acid region of homology between the C terminus of the Schizosaccharomyces pombe Sad1 protein and the Caenorhabditis elegans UNC-84 protein, SUN proteins are present in the proteomes of most eucaryotes. In addition to the SUN domain, these proteins contain a transmembrane sequence and at least one coiled-coil domain and localise to the inner nuclear envelope. SUN proteins are anchored in the inner nuclear envelope by their transmembrane segment and oriented in the membrane such that the C-terminal SUN domain is located in the space between the inner and outer nuclear membrane. Here, the SUN domain can interact with the C-terminal tail of an outer nuclear envelope protein that binds to the cytoskeleton, including the centrosome [ 1 , 2 , 3 ].

1. Comparative genomics, evolution and origins of the nuclear envelope and nuclear pore complex. Cell Cycle 3, 1612-37
2. The Sad1-UNC-84 homology domain in Mps3 interacts with Mps2 to connect the spindle pole body with the nuclear envelope. J. Cell Biol. 174, 665-75
3. Characterization of SUN-domain proteins at the higher plant nuclear envelope. Plant J. 61, 134-44