Molecular cloning of one isotype of human lamina-associated polypeptide 1s and a topological analysis using its deletion mutants.

LAP1s (lamina-associated polypeptide 1s) are type 2 integral membrane proteins with a single membrane-spanning region of the inner nuclear membrane. We report here on the cloning of the full-length cDNA of human LAP1B (huLAP1B) that encodes 584 amino acids. The sequence homology between the predicted rat LAP1B and huLAP1B was found to be 73.6%. A topological analysis was carried out by transiently expressing N-terminal GFP fused deletion mutants of huLAP1B in cells. The transmembrane (TM) domain (aa 346-368) is required for the localization of the nuclear and endoplasmic reticulum membrane and that the TM domain and the C-terminal half of the nucleoplasmic domain (aa 190-331) are sufficient for the proper localization of LAP1B. In contrast, the well-conserved lumenal domain of the nuclear membrane is not required for its topological function. Biochemical analysis showed that huLAP1B is retained within the nucleus via interactions of the nucleoplasmic portion with nuclear components. (c) 2002 Elsevier Science (USA).