Construction and properties of an Epstein-Barr-virus-derived cDNA expression vector for human cells

A cDNA expression vector containing the element oriP and the sequence encoding the Epstein-Barr virus (EBV) nuclear antigen 1 (EBNA-1) as well as the hygromycin B-resistance dominant marker gene has been constructed. Its characteristics have been compared to a similar vector lacking the EBV sequences, ( a) The EBV + vector is maintained as an episome with a copy number of approx. 50 per cell, whereas the number of the integrated EBV − copies is in general smaller than 10, when simian virus 40-transformed xeroderma pigmentosum fibroblasts (XP20S-SV) constitute the recipient cell line, ( b) The presence of the EBV sequences in the vector resulted in a five- to ten-fold higher transfection efficiency with the Ca · phosphate precipitation technique, ( c) cDNA inserts in the EBV + vector are shown to be efficiently and properly expressed in the recipient cell, ( d) If transfection is performed with a mixture of EBV + vectors with different inserts, transfectants are shown to harbour different plasmids within one cell, ( e) The ratio between these plasmids in one cell can be shifted in favour of a vector with a particular insert, when selection for this insert is performed. ( f) Reconstruction experiments indicated that isolation of a low-abundance sequence from a mixture of vectors is at least 100-fold more efficient with the EBV + system, than with the EBV − system, ( g) Rescue of the episomal vector from transfected cells can be readily achieved.