Constitutive and inducible expression of cloned human interferon-b1 gene in HeLa cells through an episomal eukaryotic vector.

An EcoRI fragment (1.83 Kb) of human DNA containing B1-interferon coding sequences was cloned in the episomal eukaryotic vector pBK-TK. The recombinant plasmid was transfected into thymidine kinase-deficient HeLa cells. Thymidine kinase-positive transformants were obtained and the cells were found to express B-interferon both constitutively and after induction with Newcastle Disease Virus or poly(rI)-poly(rC). The recombinant plasmid was present in stably transformed HeLa cells in an episomal state in hundreds of copies per cell.