Interferon-dependent induction of mRNA activity for (2'-5')oligo-isoadenylate synthetase

At least three different enzymes involved in the regulation of protein synthesis are induced in a variety of cells by interferon (IFN). Sensitive assays for these enzymes have been developed and used to establish the specificity, dose dependence and time course of their induction by IFN. One of these enzymes, the oligo-isoadenylate synthetase E, whose product (2'-5')pppApApA activates the latent ribonuclease F, is increased over 50-fold after IFN treatment. We describe here the assay for an mRNA from IFN-treated mouse L cells, that produces oligo-isoadenylate synthetase activity when injected into Xenopus oocytes. This mRNA is found in the cells only after exposure to IFN. The mRNA increases in mouse L cells with the same time course as the enzyme activity itself. In particular, there is a 3-h lag period between IFN addition and the onset of enzyme and mRNA accumulation. Using anti-IFN antibodies, we show that during this lag period the continued interaction of IFN with the cells is necessary for the full induction of the oligo-isoadenylate synthetase.