Interferon action: cytoplasmic and nuclear localization of the interferon-inducible 52-kD protein that is encoded by the Ifi 200 gene from the gene 200 cluster.

Recently, we reported that an interferon (IFN)-inducible, murine 72-kD phosphoprotein (the 204 protein) that is encoded by the Ifi 204 gene from the gene 200 cluster is localized in the nucleolus and the nucleoplasm. We have now raised a polyclonal antiserum against the 202 protein that is encoded by the Ifi 202 gene from the same gene cluster and regions of which are homologous to those from the 204 protein. Using the antiserum, we established that the 202 protein is a 52-kD phosphoprotein whose level in cells from various murine lines can be increased up to 16-fold upon treatment with IFN-alpha. Experiments involving fractionation of cell lysates and indirect immunofluorescence microscopy of cultured cells revealed that the 202 protein was localized in the cytoplasm and the nucleus. Upon treatment of cells with IFN, the 202 protein first accumulated on the surface of a cytoplasmic, membranous fraction and after prolonged treatment with IFN it was localized mainly in the nucleus. In IFN-treated mitotic AKR cells, the 202 protein was colocalized with chromosomes. 202 protein extracted from IFN-treated AKR cells bound double-stranded DNA in vitro. Studies on 202 protein function should be facilitated by the availability of complete cDNA clones and the finding of cell lines and an inbred strain of mice in which the expression of this protein was impaired.