The amino-terminal domain of the lamin B receptor is a nuclear envelope targeting signal.
The lamin B receptor (LBR) is a polytopic protein of the inner nuclear membrane. It is synthesized without a cleavable amino-terminal signal sequence and composed of a nucleoplasmic amino-terminal domain of 204 amino acids followed by a hydrophobic domain with eight putative transmembrane segments. To identify a nuclear envelope targeting signal, we have examined the cellular localization by immunofluorescence microscopy of chicken LBR, its amino-terminal domain and chimeric proteins transiently expressed in transfected COS-7. Full-length LBR was targeted to the nuclear envelope. The amino-terminal domain, without any transmembrane segments, was transported to the nucleus but excluded from the nucleolus. When the amino-terminal domain of LBR was fused to the amino-terminal side of a transmembrane segment of a type II integral membrane protein of the ER/plasma membrane, the chimeric protein was targeted to the nuclear envelope, likely the inner nuclear membrane. When the amino-terminal domain was deleted from LBR and replaced by alpha-globin, the chimeric protein was retained in the ER. These findings demonstrate that the amino-terminal domain of LBR is targeted to the nucleus after synthesis in the cytoplasm and that this polypeptide can function as a nuclear envelope targeting signal when located at the amino terminus of a type II integral membrane protein synthesized on the ER.
Soullam
B
B
Department of Medicine, Mount Sinai School of Medicine, New York 10029.
Worman
H J
HJ
D000818:Animals; D002451:Cell Compartmentation; D002460:Cell Line; D002645:Chickens; D002522:Chlorocebus aethiops; D000939:Epitopes; D005455:Fluorescent Antibody Technique; D066298:In Vitro Techniques; D008565:Membrane Proteins / Q000737:chemistry / Q000378:metabolism; D009685:Nuclear Envelope / Q000378:metabolism*; D011956:Receptors, Cell Surface / Q000737:chemistry / Q000378:metabolism*; D018160:Receptors, Cytoplasmic and Nuclear; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D011994:Recombinant Proteins / Q000378:metabolism; D014162:Transfection; D000097682:Lamin B Receptor
D000939:Epitopes; D008565:Membrane Proteins; D011956:Receptors, Cell Surface; D018160:Receptors, Cytoplasmic and Nuclear; D011993:Recombinant Fusion Proteins; D011994:Recombinant Proteins; D000097682:Lamin B Receptor