PACT, A PROTEIN ACTIVATOR OF THE INTERFERON-INDUCED PROTEIN-KINASE, PKR

PKR, a latent protein kinase, mediates the antiviral actions of interf eron, It is also involved in cellular signal transduction, apoptosis, growth regulation and differentiation. Although in virus-infected cell s, viral double-stranded (ds) RNA can serve as a PKR activator, cellul ar activators have remained obscure. Here, we report the cloning of PA CT, a cellular protein activator of PKR, PACT heterodimerized with PKR and activated it in vitro in the absence of dsRNA, In mammalian cells , overexpression of PACT caused PKR activation and, in yeast, co-expre ssion of PACT enhanced the anti-growth effect of PKR, Thus, PACT has t he hallmarks of a direct activator of PKR.