Two related Epstein-Barr virus membrane proteins are encoded by separate genes

The structures of the 2.3- and 2.0-kilobase Epstein-Barr virus (EBV) mRNAs, partially encoded within the EcoRI J fragment DNA of the viral genome, were determined by analysis of their cDNAs. Both mRNAs are transcribed across the fused terminal repeats of the EBV episome and consist of nine exons. The mRNAs are transcribed from different promoters and have a unique 5' exon from the U5 region of the genome but eight common exons from the U1 region. One principal open reading frame is present in each mRNA and is predicted to encode 54,000- and 40,000-dalton integral membrane proteins. This result was confirmed by in vitro translation of RNAs in the presence of canine pancreatic microsomes. The 2.3-kilobase mRNA is not expressed in Raji cells, owing to the deletion of the 5' regulatory and coding region of this gene, whereas neither mRNA is expressed in Namalwa cells, owing to inactivation as a result of integration of the EBV genome via the terminal repeats. Since these mRNAs are readily detected in largely latently infected cells and do not increase in abundance with EBV replication, these putative latent-infection membrane proteins are tentatively designated LMP-2A and LMP-2B, respectively.