Interferon inhibits induction of endogenous murine leukemia virus production.

In 5-iododeoxyuridine (IUDR) induction of murine leukemia virus (MLV) in Balb cells transformed by SV40 (Balb SV40) or AKR cells, interferon inhibited virus production. This could have been due to inhibition of the X- and N-tropic virus induced or to inhibition of subsequent reinfection of the mouse cells by the N tropic virus. Cycloheximide, however, activates $\text{KBalb}\text{3T3}$ cells ($\text{Balb}\text{3T3}$ cells transformed by Kirsten sarcoma virus) to produce only an X-tropic virus which could not reinfect mouse cells. In this system, interferon treatment also decreases virus yields and, therefore, an event in the virus induction process.