Expression of Epstein-Barr virus membrane antigen gp340/220 in mouse fibroblasts using a bovine papillomavirus vector

Epstein-Barr virus (EBV) membrane antigen glycoproteins gp340 and gp220 are encoded by a single gene. We have inserted this gene into a bovine papillomavirus (BPV) vector and expressed gp340/220 in mammalian cells under the control of the mouse metallothionein promoter. The proteins produced were of similar Mr, showed similar antigenic specificity and were transported to the same subcellular location as the authentic gp340/220. The inclusion of heavy metal ions in the medium had no effect on the levels of gp340/220, which were approximately the same as those found in standard EBV-transformed lymphoblastoid cell lines, e.g. B95-8. Cells that expressed gp340/220 were selected by several rounds of fluorescence-activated cell sorting, but on passage they rapidly lost the ability to express this glycoprotein. In contrast to this we found that BPV-transformed cells expressing a truncated version of gp340/220 still produced it at significant levels after extended passage.