Le interferon mRNA from human fibroblasts.

Human F and Le interferon can be clearly distinguished on the basis of different antigenic properties and host range. After inoculation with Newcastle disease virus (NDV), GM-258 fibroblasts produced Le as well as F interferon; in contrast, only F interferon was detectable after stimulation with poly(I) . poly(C). Polyadenylylated mRNA isolated from fibroblasts induced with poly(I) . poly(C) or NDV was injected into Xenopus laevis oocytes and the interferon activities thus produced were analyzed. Only F interferon production was demonstrable in oocytes injected with mRNA from cells induced with poly(I) . poly(C), whereas both F and Le interferons were made in oocytes injected with mRNA from NDV-induced cultures. The time course of accumulation of F and Le interferon mRNAs in NDV-induced cells corresponded to the kinetics of F and Le interferon synthesis in intact cells. The ratio of F and Le interferons made in oocytes was similar to that observed in intact GM-258 cells. F and Le interferon mRNA activities isolated from GM-258 cells could not be separated by sucrose density gradient centrifugation. However, the profile of F mRNA activity was more heterogeneous and its peak sedimented somewhat more slowly than that of Le interferon mRNA. These results suggest that the varying ratios of F and Le interferon synthesis in different cells after different modes of stimulation are determined at the level of mRNA. The induction mechanisms of F and Le interferon mRNA synthesis appear to be closely related but not identical.