An EBV-based mammalian cell expression vector for efficient expression of cloned coding sequences.

The construction of a mammalian cell expression vector using human cytomegalovirus immediate early gene enhancer to initiate transcription of inserted coding sequences is described. The vector also carries Epstein-Barr virus EBNA-1 nuclear antigen gene, ori-P sequences and hygromycin B resistance gene hph from E. coli. The expression capacity of this construct was tested by inserting the chloramphenicol acetyltransferase (CAT) gene into the vector. The EBV-CAT construct was transfected into various cell lines and high levels of CAT activity were obtained in human and monkey cells. In these cells, the vector DNA also replicates as an extrachromosomal element having 1 to 20 copies per cell. In most cases, the vector copy number and the expression level of inserted gene was in positive correlation in different cell clones.