title: The role of sequences unique to nuclear intermediate filaments in the targeting and assembly of human lamin B: evidence for lack of interaction of lamin B with its putative receptor.
abstract: The mechanism by which human nuclear lamin B is targeted and assembled has been studied by transfecting into mammalian cells lamin mutants deleted of three sequences unique to lamins. Nuclear lamins contain an extra 42 amino acids (aa) in their rod domains and NLS and CAAX motifs in their tail domains, which distinguishes them from cytoplasmic IF proteins. These three sequences act in concert to ensure correct temporal and spatial assembly of lamin B. Deletion of any one of these three sequences from lamin B did not significantly disrupt nuclear lamina targeting, but when two or more of these sequences were deleted, targeting was severely compromised. The CAAX motif is necessary for the efficient integration of lamin B into an already formed nuclear lamina, since lamin B CAAX- mutants had reduced targeting to the lamina when arrested in S phase of the cell cycle. CAAX-deficient mutant lamin B proteins were soluble and not associated with membranes at mitosis, proving that the CAAX motif is responsible for association of human lamin B with membranes. In addition, CAAX- mutant lamin B proteins fractionated independently of the lamin B-receptor (LBR), indicating that these two proteins do not bind directly to each other.
authors.affiliation: Department of Molecular Biology and Biophysics, Medical Biotechnology Center and Department of Neurology, Molecular and Cell Biology Graduate Program, University of Maryland, Baltimore, Maryland 21201, USA.
authors.forename: T I
authors.initials: TI
authors.lastname: Mical
authors.forename: M J
authors.initials: MJ
authors.lastname: Monteiro
mesh_terms: D016475:3T3 Cells; D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D002460:Cell Line; D017931:DNA Primers / Q000235:genetics; D006367:HeLa Cells; D006801:Humans; D007381:Intermediate Filament Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D034921:Lamin Type B; D034882:Lamins; D051379:Mice; D008954:Models, Biological; D008969:Molecular Sequence Data; D009685:Nuclear Envelope / Q000378:metabolism; D019913:Nuclear Localization Signals; D009687:Nuclear Proteins / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism*; D011485:Protein Binding; D018160:Receptors, Cytoplasmic and Nuclear / Q000378:metabolism*; D017384:Sequence Deletion; D014162:Transfection; D000097682:Lamin B Receptor
chemical_list: D017931:DNA Primers; D007381:Intermediate Filament Proteins; D034921:Lamin Type B; D034882:Lamins; D019913:Nuclear Localization Signals; D009687:Nuclear Proteins; D018160:Receptors, Cytoplasmic and Nuclear; D000097682:Lamin B Receptor