Mechanism of interferon action. The interferon-induced phosphoprotein P1 possesses a double-stranded RNA-dependent...

Protein P1, the interferon-induced protein phosphorylated in the presence of dsRNA in human amnion U-cells, was covalently labeled with [alpha-32P]ATP following ultraviolet irradiation. The photoaffinity labeling of protein P1 was dependent upon double-stranded RNA. Antibody prepared against phosphorylated protein P1 immunoprecipitated the double-stranded RNA-dependent photoaffinity-labeled product. The extent of photoaffinity labeling was significantly decreased by the addition of unlabeled ATP, GTP, or AMP; adenosine had little effect on the photoaffinity labeling of protein P1. These results suggest that protein P1 possesses a site capable of binding an adenine nucleotide in a double-stranded RNA-dependent manner.