Interferon inhibits transformation of mouse cells by exogenous cellular or viral genes.

Specific genes can be introduced into cultured mammalian cells by DNA transfer1, sometimes to be stably integrated and expressed2,3. Because interferon inhibits the transformation initiated by DNA viruses4–8, we wondered if it might also affect transformation induced by recombinant plasmids and cellular genes. We show here that in mouse L cells interferon treatment prevents stable integration and expression of the transfected plasmids containing the cloned herpesvirus thymidine kinase (tk) gene, or the dihydrofolate reductase (dhfr) gene from hamster ovary cells9. In contrast, interferon does not prevent transient expression of the tk gene in unintegrated form.