Characterisation of the interferon-mediated protein kinase by polyclonal antibodies

Interferon-treated human cells show an enhanced level of a double-stranded (ds) RNA-dependent protein kinase activity which is manifested by the phosphorylation of an endogenous 72,000 molecular weight protein (p72K kinase). By the use of murine polyclonal antibodies against this p72K kinase, here we have characterized the protein kinase activity associated with immune complexes precipitated from extracts of interferon-treated cells. Precipitation of the p72K kinase by the polyclonal antibodies results in the formation of a complex in which the kinase activity is manifested by phosphorylation of the 72K protein. This phosphorylation, however, is independent of dsRNA. Such immunoprecipitates can also phosphorylate exogenous substrates, calf thymus histones and the alpha subunit of protein initiation factor eIF2.