Determinants for intracellular sorting of cytoplasmic and nuclear intermediate filaments.
The mechanism by which nuclear and cytoplasmic filaments are sorted in vivo was studied by examining which lamin sequences are required to target an otherwise cytoplasmic IF protein, the small neurofilament subunit (NF-L), to the nuclear lamina. By swapping corresponding domains between NF-L and lamin A, nuclear envelope targeting of NF-L was shown to require the presence of the "head" domain, a 42-amino acid sequence unique to lamin rod domains, a nuclear localization signal and the CAAX motif. Replacement of the entire COOH-terminal tail of lamin A with that of NF-L had no discernible effect on nuclear localization of lamin A, provided the substituted NF-L tail contained a NLS and a CAAX motif. This chimeric protein exhibited characteristics more typical of lamin B than that of the parental lamin A. With regard to cytoplasmic assembly properties, substitution of the head domain of lamin A for that of NF-L did not substantially affect the ability of NF-L to coassemble with vimentin in the cytoplasm. In contrast, insertion of a 42-amino acid sequence unique to lamin rod domains into NF-L profoundly affected NF-L coassembly with vimentin indicating that the 42-amino acid insertion in lamins may be important for sorting lamins from cytoplasmic IF proteins.
Medical Biotechnology Center, University of Maryland Biotechnology Institute, Baltimore.
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Monteiro
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Hicks
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Gu
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Janicki
D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D001692:Biological Transport; D002451:Cell Compartmentation; D002460:Cell Line; D003593:Cytoplasm / Q000378:metabolism*; D006801:Humans; D007382:Intermediate Filaments / Q000378:metabolism* / Q000648:ultrastructure; D007739:L Cells; D034904:Lamin Type A; D034921:Lamin Type B; D034882:Lamins; D051379:Mice; D018613:Microscopy, Confocal; D008856:Microscopy, Fluorescence; D008969:Molecular Sequence Data; D016900:Neurofilament Proteins / Q000737:chemistry / Q000378:metabolism*; D009685:Nuclear Envelope / Q000378:metabolism* / Q000648:ultrastructure; D009687:Nuclear Proteins / Q000737:chemistry / Q000378:metabolism*; D011993:Recombinant Fusion Proteins / Q000737:chemistry / Q000378:metabolism; D014162:Transfection; D014746:Vimentin / Q000378:metabolism
D034904:Lamin Type A; D034921:Lamin Type B; D034882:Lamins; D016900:Neurofilament Proteins; D009687:Nuclear Proteins; D011993:Recombinant Fusion Proteins; D014746:Vimentin; C044882:neurofilament protein L