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Epstein-Barr virus glycoprotein homologous to herpes simplex virus gB
Insights
The Epstein-Barr virus BALF4 gene encodes gp110, an abundant glycoprotein found in the cytoplasm and intracellular membranes of infected cells. This protein, likely involved in modifying infected membranes, differs in localization from herpes simplex virus gB.
Area of Science:
- Virology
- Molecular Biology
- Cell Biology
Background:
- Epstein-Barr virus (EBV) is a human herpesvirus associated with various diseases.
- The BALF4 open reading frame of EBV shares sequence similarity with herpes simplex virus glycoprotein B (HSV gB).
Purpose of the Study:
- To characterize the protein encoded by the EBV BALF4 gene.
- To investigate the synthesis, glycosylation, and cellular localization of the EBV BALF4 protein.
Main Methods:
- Nucleotide sequence comparison.
- In vitro transcription and translation.
- Metabolic labeling with tunicamycin and immunoprecipitation.
- N-glycosidase F treatment.
- Immunofluorescence microscopy.
Main Results:
- The EBV BALF4 gene encodes a 110-kilodalton glycoprotein (gp110).
- A 93-kilodalton precursor to gp110 was identified.
- gp110 exhibits both N- and O-linked glycosylation.
- gp110 is abundant in EBV-infected cells, localized primarily in the cytoplasm, perinuclear region, nuclear membranes, and endoplasmic reticulum.
- gp110 was not detected in the infected-cell plasma membrane, unlike HSV gB.
Conclusions:
- EBV gp110 is a major glycoprotein synthesized during the late infectious cycle.
- gp110's localization suggests a role in modifying intracellular membranes during EBV replication.
- EBV gp110 has distinct cellular localization compared to HSV gB.
Abstract:
The Epstein-Barr virus DNA open reading frame BALF4 (R. Baer, A.T. Bankier, M.D. Biggin, P.L. Deininger, P.J. Farrell, T.J. Gibson, G. Hatfull, G.S. Hudson, S.C. Stachwell, C. Sequin, P.S. Tuffnell, and B.G. Barrell, Nature [London] 310:207-211, 1984), which by nucleotide sequence comparison could encode a protein similar to herpes simplex virus gB (P.E. Pellett, M.D. Biggin, B. Barrell, and B. Roizman, J. Virol. 56:807-813, 1985), has now been shown to encode a 110-kilodalton glycoprotein. Late infectious cycle RNAs of 3.0 and 1.8 kilobases are transcribed from BALF4. Translation of these RNAs in vitro, transcription and translation of BALF4 in vitro, or metabolic labeling of cells in the presence of tunicamycin and immunoprecipitation with BALF4-specific sera results in identification of a 93-kilodalton precursor to gp110. Since N-glycosidase F only reduces the size of gp110 to 105 kilodaltons, gp110 probably has both N- and O-linked glycosylation, gp110 is an abundant glycoprotein in Epstein-Barr virus-infected cells. In infected lymphocytes and in 3T3 cells, in which the gene is expressed from a recombinant expression vector, most of the protein is cytoplasmic and perinuclear. In contrast to gB, gp110 was not detected in the infected-cell plasma membrane. In cells replicating Epstein-Barr virus, gp110 localized to the inner and outer nuclear membrane lamellae and to endoplasmic reticulum structures which sometimes contained enveloped virus. gp110 may play an important role in modifying infected intracellular membranes.