MAN1, an inner nuclear membrane protein that shares the LEM domain with lamina-associated polypeptide 2 and emerin

The "MAN antigens" are polypeptides recognized by autoantibodies from a pat ient with a collagen vascular disease and localized to the nuclear envelope . We now show that one of the human MAN antigens termed MAN1 is a 82.3-kDa protein with an amino-terminal domain followed by two hydrophobic segments and a carboxyl-terminal tail. The MAN1 gene contains seven protein-coding e xons and is assigned to human chromosome 12q14, Its mRNA is approximately 5 .5 kilobases and is detected in several different cell types that were exam ined. Cell extraction experiments show that MAN1 is an integral membrane pr otein, When expressed in transfected cells, MAN1 is exclusively targeted to the nuclear envelope, consistent with an inner nuclear membrane localizati on. Protein sequence analysis reveals that MAN1 shares a conserved globular domain of approximately 40 amino acids, which we term the LEM module, with inner nuclear membrane proteins lamina-associated polypeptide 2 and emerin . The LEM module is also present in two proteins of Caenorhabditis elegans. These results show that MAN1 is an integral protein of the inner nuclear m embrane that shares the LEM module with other proteins of this subcellular localization.