An interferon-inducible, RNA-dependent protein serine/threonine kinase
(PKR) has been described. PKR in earlier literature is variously known as DAI,
dsJ, PI kinase, p65, p67 or TIK for the mouse kinase; and p68 or p69 for the
human kinase. The PKR kinase substrate is the α subunit of protein synthesis
initiation factor eIF-2. Phosphorylation of eIF-2α on serine-51 results in
inhibition of translation. Molecular cDNA clones have been isolated from
both human and mouse cells. The serine/threonine kinase catalytic domains
map to the carboxy terminal half of the protein while the RNA-binding
domains are located in the amino terminal region. Three kinds of regulation
of PKR enzymatic activity have been described. These include transcriptional
regulation in response to interferon, an autoregulatory mechanism controlling
PKR expression at the level of translation and post-translational regulation
by RNA mediated autophosphorylation.