Identification and sequence of an accessory factor required for activation of the human interferon γ receptor

Human chromosomes 6 and 21 are both necessary to confer sensitivity to human interferon γ (Hu-IFN-γ), as measured by induction of class I human leukocyte antigen (HLA) and protection against encephalomyocarditis virus (EMCV) infection. Whereas human chromosome 6 encodes the Hu-IFN-γ receptor, human chromosome 21 encodes accessory factors for generating biological activity through the Hu-IFN-γ receptor. Probes from a genomic clone were used to identity cDNA clones expressing a species-specific accessory factor. These cDNA clones are able to substitute for human chromosome 21 to reconstitute the Hu-IFN-γ receptor-mediated induction of class I HLA antigens. However, the factor encoded by the cDNA does not confer full antiviral protection against EMCV, confirming that an additional factor encoded on human chromosome 21 is required for reconstitution of antiviral activity against EMCV. We conclude that this accessory factor belongs to a family of such accessory factors responsible for different actions of IFN-γ.