title: Is the 6 kDa tobacco etch viral protein a bona fide ERES marker?
abstract: The claim that the 6 kDa viral protein (VP) of Tobacco Etch Virus is a marker for ER exit sites (ERES) has been investigated. When transiently expressed as a CFP tagged fusion construct in tobacco mesophyll protoplasts, this integral membrane protein co-localizes with both the COPII coat protein YFP-SEC24 and the Golgi marker Man1-RFP. However, when over-expressed the VP locates to larger spherical structures which co-localize with neither ER nor Golgi markers. Nevertheless, deletion of the COPII interactive N-terminal D(X)E motif causes it to be broadly distributed throughout the ER, supporting the notion that this protein could be an ERES marker. Curiously, whereas brefeldin A (BFA) caused a typical Golgi-stack response (redistribution into the ER) of the VP in leaf epidermal cells, in protoplasts it resulted in the formation of structures identical to those formed by over-expression. However, anomalous results were obtained with protoplasts: when co-expressed with the non-cycling cis-Golgi marker Man1-RFP, a BFA-induced redistribution of the VP-CFP signal into the ER was observed, but, in the presence of the cycling Golgi marker ERD2-YFP, this did not occur. High resolution images of side-on views of Golgi stacks in epidermal cells showed that the 6 kDa VP-CFP signal overlapped considerably more with YFP-SEC24 than with Man1-RFP, indicating that the VP is proportionately more associated with ERES. However, based on a consideration of the structure of its cytoplasmic tail, the scenario that the VP collects at ERES and is transported to the cis-Golgi before being recycled back to the ER, is supported.
authors.affiliation: Department of Plant Cell Biology, Centre for Organismal Studies, University of Heidelberg, Germany.
authors.forename: Alexander
authors.initials: A
authors.lastname: Lerich
authors.forename: Markus
authors.initials: M
authors.lastname: Langhans
authors.forename: Silke
authors.initials: S
authors.lastname: Sturm
authors.forename: David G
authors.initials: DG
authors.lastname: Robinson
mesh_terms: D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D015415:Biomarkers / Q000378:metabolism; D022181:COP-Coated Vesicles / Q000378:metabolism / Q000821:virology; D004721:Endoplasmic Reticulum / Q000821:virology*; D006056:Golgi Apparatus / Q000378:metabolism; D008969:Molecular Sequence Data; D010935:Plant Diseases / Q000821:virology*; D017800:Potyvirus / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D021381:Protein Transport; D014026:Nicotiana / Q000821:virology*; D014764:Viral Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*
chemical_list: D015415:Biomarkers; D014764:Viral Proteins