The mouse TIK protein, a serine/threonine kinase, was originally isolated from a murine pre-B cell expression library by its ability to bind anti-phosphotyrosine antibodies (Icely et al., J. Biol. Chem. 266, 16073 -16077,1991). The 67 kDa protein was found to have an associated autophosphorylation activity when incubated with ATP. Our results show that TIK is actually the mouse interferon-induced, dsRNAdependent protein kinase, PKR. We demonstrate that the TIK message is interferon-inducible in mouse Lcells and in vitro transcription and translation of the TIK cDNA produces a protein that is capable of binding double-stranded RNA. The in vitro synthesized TIK protein migrated as a 65 kDa protein on SDS-PAGE when incubated with ATP, but migrated as a 60 kDa protein when incubated with an inhibitor of PKR, 2-aminopurine. We further show that proteolytic digestion of TIK with Staphylococcus aureus V8 protease results in a cleavage pattern identical to that obtained by V8 digestion of authentic PKR. Antiserum to TIK specifically recognized PKR. Cloned TIK had inhibitory activity for replication of EMCV but not VSV. From these observations we conclude that TIK kinase is the mouse interferon-induced, double-stranded RNAdependent kinase, PKR.
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