SUN (Sad1p, UNC-84) domains are conserved C-terminal protein regions a few hundred amino acids long.
Most proteins containing SUN domains are thought to be involved in the positioning of the nucleus in the cell.
It is thought that SUN domains interact directly with KASH domains in the space between the outer and inner nuclear membranes to bridge the nuclear envelope and transfer force from the nucleoskeleton to the cytoplasmic cytoskeleton which enables mechanosensory roles in cells.
[1] SUN proteins are thought to localize to the inner nuclear membrane.
[3][4] Caenorhabditis elegans Drosophila melanogaster Mammals Schizosaccharomyces pombe Saccharomyces cerevisiae Maize Arabidopsis