Epstein-Barr virus mRNA export factor EB2 is essential for production of infectious virus.
The splicing machinery which positions a protein export complex near the exon-exon junction mediates nuclear export of mRNAs generated from intron-containing genes. Many Epstein-Barr virus (EBV) early and late genes are intronless, and an alternative pathway, independent of splicing, must export the corresponding mRNAs. Since the EBV EB2 protein induces the cytoplasmic accumulation of intronless mRNA, it is tempting to speculate that EB2 is a viral adapter involved in the export of intronless viral mRNA. If this is true, then the EB2 protein is essential for the production of EBV infectious virions. To test this hypothesis, we generated an EBV mutant in which the BMLF1 gene, encoding the EB2 protein, has been deleted (EBV(BMLF1-KO)). Our studies show that EB2 is necessary for the production of infectious EBV and that its function cannot be transcomplemented by a cellular factor. In the EBV(BMLF1-KO) 293 cells, oriLyt-dependent DNA replication was greatly enhanced by EB2. Accordingly, EB2 induced the cytoplasmic accumulation of a subset of EBV early mRNAs coding for essential proteins implicated in EBV DNA replication during the productive cycle. Two herpesvirus homologs of the EB2 protein, the herpes simplex virus type 1 protein ICP27 and, the human cytomegalovirus protein UL69, only partly rescued the phenotype of the EBV(BMLF1-KO) mutant, indicating that some EB2 functions in virus production cannot be transcomplemented by ICP27 and UL69.
Laboratoire de Virologie Humaine, INSERM U412, ENS-Lyon, F-69364 Lyon Cedex 07, France. hgruffat@ens-lyons.fr
Henri
H
Gruffat
Julien
J
Batisse
Dagmar
D
Pich
Bernhard
B
Neuhierl
Evelyne
E
Manet
Wolfgang
W
Hammerschmidt
Alain
A
Sergeant
D021581:Active Transport, Cell Nucleus; D000595:Amino Acid Sequence; D004261:DNA Replication; D004268:DNA-Binding Proteins / Q000235:genetics; D004259:DNA-Directed DNA Polymerase / Q000235:genetics; D004854:Herpesvirus 4, Human / Q000502:physiology*; D008969:Molecular Sequence Data; D010750:Phosphoproteins / Q000502:physiology*; D012333:RNA, Messenger / Q000032:analysis / Q000378:metabolism; D015534:Trans-Activators / Q000502:physiology*; D014764:Viral Proteins / Q000235:genetics / Q000502:physiology*; D014779:Virus Replication
C096364:BALF2 protein, Human herpesvirus 4; D004268:DNA-Binding Proteins; D010750:Phosphoproteins; D012333:RNA, Messenger; C090236:SM protein, Human herpesvirus 4; D015534:Trans-Activators; D014764:Viral Proteins; C083202:BALF5 protein, Epstein-barr virus; D004259:DNA-Directed DNA Polymerase