THE LONG AMINO-TERMINAL TAIL DOMAIN OF ANNEXIN-XI IS NECESSARY FOR ITS NUCLEAR-LOCALIZATION

Annexin XI is a newly identified annexin which localizes mainly in the nucleus of rat embryonic fibroblasts. There are no typical nuclear lo calization signals (NLS) in the molecule. To define the region respons ible for its nuclear localization, a series of mutants and chimeric cD NA were constructed. These were transiently expressed in COS-7 cells, and the subcellular distributions of the mutants and chimeric proteins were determined by indirect immunofluorescence microscopy. Wild-type annexin XI was located predominantly within the nucleus. Deletion of t he N-terminal tail domain (residues 3-196) changed the distribution of the protein from the nucleus to the cytoplasm whereas deletion of the C-terminal core domain (residues 208-504) still kept the protein sort ing to the nucleus. Three other mutants lacking 60-80 amino acids in t he N-terminal region (residues 3-61, 61-115, and 115-197, respectively ) no longer efficiently imported into the nucleus. Furthermore, Escher ichia coli beta-galactosidase polypeptide was efficiently localized to the nucleus only when fused with the whole N-terminal region of annex in XI (residues 1-207), not with part of the N-terminal region. In pri mary cultured rat hepatocytes, annexin XI was distributed in the cytop lasm but not in the nucleus. These results suggest that the whole N-te rminal tail domain of annexin XI is necessary and sufficient for its n uclear localization, and may function as NLS in a cell-type specific m anner. (C) 1995 Academic Press, Inc.