A second Epstein-Barr virus membrane protein (LMP2) is expressed in latent infection and colocalizes with LMP1

Recent cDNA cloning and sequencing of two Epstein-Barr virus (EBV)-specific mRNAs from latently infected cultures revealed that these RNAs are encoded across the fused terminal repeats of the viral genome and that they are likely to encode two nearly identical proteins with the same transmembrane domains. The smaller predicted protein (LMP2B) lacks 119 amino-terminal amino acids found in the larger one (LMP2A). To test whether these proteins are expressed in latently infected lymphocytes, antibodies to the LMP2 proteins were derived by immunizing rabbits with TrpE-LMP2A fusion proteins. Affinity-purified LMP2-specific antibodies recognized 54- and 40-kilodalton proteins, corresponding to LMP2A and LMP2B, in immunoblots of rodent fibroblasts stably transfected with eucaryotic expression plasmids containing either the LMP2A or LMP2B cDNA. Similar-size proteins were also identified in immunoblots of latently infected lymphocytes. LMP2A localized to membranes in cellular fractionation studies. In immunofluorescent studies, LMP2 localized in the plasma membrane of EBV-infected lymphocytes, with the majority of reactivity confined to the region of the LMP1 patch. This reactivity was detected in almost all lymphoblastoid cells latently infected with EBV.