The first membrane spanning region of the lamin B receptor is sufficient for sorting to the inner nuclear membrane.
The lamin B receptor (LBR) is a polytopic integral membrane protein localized exclusively in the inner nuclear membrane domain of the nuclear envelope. Its cDNA deduced primary structure consists of a highly charged amino-terminal domain of 205 residues that faces the nucleoplasm followed by a hydrophobic domain with eight potential transmembrane segments. To identify determinants that sort LBR from its site of integration (RER and outer nuclear membrane) to the inner nuclear membrane, we prepared full-length, truncated, and chimeric cDNA constructs of chick LBR, transfected these into mammalian cells and detected the expressed protein by immunofluorescence microscopy using appropriate antibodies. Surprisingly, we found that the determinants for sorting of LBR to the inner nuclear membrane reside in a region comprising its first transmembrane sequence plus flanking residues on either side. The other transmembrane regions as well as the nucleoplasmic domain are not required for sorting. We propose that the first transmembrane segment of LBR interacts specifically with another transmembrane segment and consider several mechanisms by which such specific interaction could result in sorting to the inner nuclear membrane.
Smith
S
S
Laboratory of Cell Biology, Howard Hughes Medical Institute, Rockefeller University, New York 10021.
Blobel
G
G
D000818:Animals; D001483:Base Sequence; D002460:Cell Line; D002645:Chickens; D003001:Cloning, Molecular; D008861:Microsomes / Q000378:metabolism*; D008969:Molecular Sequence Data; D009685:Nuclear Envelope / Q000378:metabolism*; D009838:Oligodeoxyribonucleotides; D010957:Plasmids; D016133:Polymerase Chain Reaction / Q000379:methods; D014176:Protein Biosynthesis; D011487:Protein Conformation; D011499:Protein Processing, Post-Translational; D011956:Receptors, Cell Surface / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D018160:Receptors, Cytoplasmic and Nuclear; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D015183:Restriction Mapping; D012273:Ribulose-Bisphosphate Carboxylase / Q000235:genetics / Q000378:metabolism; D014158:Transcription, Genetic; D014162:Transfection; D000097682:Lamin B Receptor
D009838:Oligodeoxyribonucleotides; D011956:Receptors, Cell Surface; D018160:Receptors, Cytoplasmic and Nuclear; D011993:Recombinant Fusion Proteins; D012273:Ribulose-Bisphosphate Carboxylase; D000097682:Lamin B Receptor