Two interferon-induced proteins are involved in the protein kinase complex dependent on double-stranded RNA.

The double-stranded (ds) RNA-dependent protein kinase is a 100,000-110,000 Mr complex of two interferon-induced subunits each having ATP binding sites: a 48,000 Mr protein (p48) which appears to be responsible for the phosphorylation of a 68,000 Mr protein (p68) in the presence of dsRNA. The p68 subunit once phosphorylated is converted to an active protein kinase capable of phosphorylating exogenous substrates such as the alpha subunit of protein synthesis initiation factor eIF2 or calf thymus histone. The phosphorylation of exogenous substrates is highly correlated with the degree of phosphate saturation of p68 and does not require the presence of dsRNA. Both the p68 and the p48 subunits of the protein kinase complex are purified by an immuno-affinity column containing monoclonal antibody specific for the p68 subunit.