title: Sec61alpha and TRAM are sequentially adjacent to a nascent viral membrane protein during its ER integration.
abstract: Co-translational integration of a nascent viral membrane protein into the endoplasmic reticulum membrane takes place via the translocon. We have been studying the early stages of the integration of a double-spanning plant viral movement protein to gain insights into how viral membrane proteins are transferred from the hydrophilic interior of the translocon into the hydrophobic environment of the bilayer, where the transmembrane (TM) segments of the viral proteins can diffuse freely. Photocrosslinking experiments reveal that this integration involves the sequential passage of the TM segments past Sec61alpha and translocating chain-associating membrane protein (TRAM). Each TM segment is first adjacent to Sec61alpha and subsequently is adjacent to TRAM. TRAM crosslinking extends for a long period during nascent chain biogenesis. In addition, the replacement of the first viral TM segment with a non-viral TM sequence still yields nascent chain photo-adducts with TRAM. TRAM therefore appears to be involved in viral membrane protein integration, and nascent chain recognition by TRAM does not appear to rely solely on the TM domains.
authors.affiliation: Departament de Bioquímica i Biologia Molecular, Universitat de València. E-46 100 Burjassot, Spain.
authors.forename: Ana
authors.initials: A
authors.lastname: Saurí
authors.forename: Peter J
authors.initials: PJ
authors.lastname: McCormick
authors.forename: Arthur E
authors.initials: AE
authors.lastname: Johnson
authors.forename: Ismael
authors.initials: I
authors.lastname: Mingarro
mesh_terms: D000818:Animals; D003432:Cross-Linking Reagents / Q000494:pharmacology; D004285:Dogs; D004721:Endoplasmic Reticulum / Q000378:metabolism*; D008562:Membrane Glycoproteins / Q000235:genetics*; D008565:Membrane Proteins / Q000235:genetics*; D008954:Models, Biological; D018832:Molecular Chaperones / Q000235:genetics*; D053830:Plant Viral Movement Proteins / Q000235:genetics; D012333:RNA, Messenger / Q000235:genetics; D000069816:SEC Translocation Channels; D014763:Viral Matrix Proteins / Q000235:genetics* / Q000502:physiology; D016662:Virus Integration
chemical_list: D003432:Cross-Linking Reagents; D008562:Membrane Glycoproteins; D008565:Membrane Proteins; D018832:Molecular Chaperones; D053830:Plant Viral Movement Proteins; D012333:RNA, Messenger; D000069816:SEC Translocation Channels; D014763:Viral Matrix Proteins; C096099:nascent-polypeptide-associated complex; C074282:translocating chain-associating membrane protein (TRAM)