Identification of a novel signal sequence that targets transmembrane proteins to the nuclear envelope inner membrane.
Herpesvirus maturation requires translocation of glycoprotein B homologue from the endoplasmic reticulum to the inner nuclear membrane. Glycoprotein B of human cytomegalovirus was used in this context as a model protein. To identify a specific signal sequence within human cytomegalovirus glycoprotein B acting in a modular fashion, coding sequences were recombined with reporter proteins. Immunofluorescence and cell fractionation demonstrated that a short sequence element within the cytoplasmic tail of human cytomegalovirus glycoprotein B was sufficient to translocate the membrane protein CD8 to the inner nuclear membrane. This carboxyl-terminal sequence had no detectable nuclear localization signal activity for soluble beta-Galactosidase and could not be substituted by the nuclear localization signal of SV40 T antigen. For glycoprotein B of herpes simplex virus, a carboxyl-terminal element with comparable properties was found. Further experiments showed that the amino acid sequence DRLRHR of human cytomegalovirus glycoprotein B (amino acids 885-890) was sufficient for nuclear envelope translocation. Single residue mutations revealed that the arginine residues in positions 4 and 6 of the DRLRHR sequence were essential for its function. These results support the view that transmembrane protein transport to the inner nuclear membrane is controlled by a mechanism different from that of soluble proteins.
Meyer
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Institut für Virologie der Philipps-Universität, Robert-Koch-Strasse 17, 35037 Marburg, Germany.
Radsak
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KD
D000595:Amino Acid Sequence; D000952:Antigens, Polyomavirus Transforming / Q000378:metabolism; D016827:CD8 Antigens / Q000378:metabolism; D003587:Cytomegalovirus; D005455:Fluorescent Antibody Technique; D018259:Herpesvirus 1, Human / Q000378:metabolism; D008565:Membrane Proteins / Q000378:metabolism*; D008969:Molecular Sequence Data; D009685:Nuclear Envelope / Q000378:metabolism*; D021382:Protein Sorting Signals; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D014759:Viral Envelope Proteins / Q000378:metabolism
D000952:Antigens, Polyomavirus Transforming; D016827:CD8 Antigens; D008565:Membrane Proteins; D021382:Protein Sorting Signals; D011993:Recombinant Fusion Proteins; D014759:Viral Envelope Proteins; C040495:glycoprotein B, Simplexvirus