title: The hepatitis C virus nonstructural protein 4B is an integral endoplasmic reticulum membrane protein.
abstract: The hepatitis C virus (HCV) nonstructural protein 4B (NS4B) is a relatively hydrophobic 27-kDa protein of unknown function. A tetracycline-regulated gene expression system, a novel monoclonal antibody, and in vitro transcription-translation were employed to investigate the subcellular localization and to characterize the membrane association of this viral protein. When expressed individually or in the context of the entire HCV polyprotein, NS4B was localized in the endoplasmic reticulum (ER), as shown by subcellular fractionation, immunofluorescence analyses, and double-label confocal laser scanning microscopy. In this compartment NS4B colocalized with the other HCV nonstructural proteins. Association of NS4B with the ER membrane occurred cotranslationally, presumably via engagement of the signal recognition particle by an internal signal sequence. In membrane extraction and proteinase protection assays NS4B displayed properties of a cytoplasmically oriented integral membrane protein. Taken together, our findings suggest that NS4B is a component of a membrane-associated cytoplasmic HCV replication complex. An efficient replication system will be essential to further define the role of NS4B in the viral life cycle.
authors.affiliation: Department of Medicine II, University of Freiburg, Freiburg, D-79106, Germany.
authors.forename: T
authors.initials: T
authors.lastname: Hügle
authors.forename: F
authors.initials: F
authors.lastname: Fehrmann
authors.forename: E
authors.initials: E
authors.lastname: Bieck
authors.forename: M
authors.initials: M
authors.lastname: Kohara
authors.forename: H G
authors.initials: HG
authors.lastname: Kräusslich
authors.forename: C M
authors.initials: CM
authors.lastname: Rice
authors.forename: H E
authors.initials: HE
authors.lastname: Blum
authors.forename: D
authors.initials: D
authors.lastname: Moradpour
mesh_terms: D000818:Animals; D000911:Antibodies, Monoclonal; D004721:Endoplasmic Reticulum / Q000378:metabolism* / Q000821:virology; D004797:Enzyme-Linked Immunosorbent Assay; D019084:Fluorescent Antibody Technique, Indirect; D015967:Gene Expression Regulation, Viral; D016174:Hepacivirus / Q000472:pathogenicity*; D008565:Membrane Proteins / Q000378:metabolism*; D051379:Mice; D008807:Mice, Inbred BALB C; D018613:Microscopy, Confocal; D014176:Protein Biosynthesis; D013752:Tetracycline / Q000494:pharmacology; D014158:Transcription, Genetic; D017361:Viral Nonstructural Proteins / Q000378:metabolism*; D014764:Viral Proteins / Q000378:metabolism*
chemical_list: D000911:Antibodies, Monoclonal; D008565:Membrane Proteins; C093542:NS4 protein, hepatitis C virus; D017361:Viral Nonstructural Proteins; D014764:Viral Proteins; D013752:Tetracycline