The first membrane spanning region of the lamin B receptor is sufficient for sorting to the inner nuclear membrane

p58cDNA. A full-length cDNA consisting of the 5' untranslated region, codons 1 through 637, and the 3' untranslated region was generated from two overlapping clones, DJ-5 and M-3, described previously , by ligation at a common internal, unique AceI site and cloned into the EcoRI site of Bluescript SK-(Stratagene, La Jolla, CA). pSVX. A fragment containing a translational stop eodon in all three read-ing frames was generated using complementary oligonucleotides, 5'-TCG-ATGACCTATGAACTATGAGCTA-3' and 5'-TCGATAGCTCATAGTrCA-TAGGTCA-3', and inserted into the XhoI site in the pulyllnker of the SV-40based expression vector, pSVK3 (Pharmacia Fine Chemicals, Piscataway, NJ). All truncated constructs were expressed in the pSVX vector to ensure that there was a stop codon at the end of the open reading frame.