Specific mutations near the amino terminus of double-stranded RNA-dependent protein kinase (PKR) differentially affect its double-stranded RNA binding and dimerization properties

The amino-terminal region of the double-stranded (ds) RNA-dependent protein kinase, PKR, has been shown to mediate both dsRNA binding and protein dimerization, To critically examine if PKR dimerization is dependent on dsRNA binding, we generated a series of mutants that are incapable of binding dsRNA. Some, but not all, of these mutants retained the ability to dimerize, as shown by a two-hybrid transcriptional activation assay in vivo and a chemical cross-linking assay in vitro. These mutants were used further to demonstrate that the translational inhibitory activity of PKR in vivo requires dsRNA binding; PKR mutants that dimerized but did not bind dsRNA could not inhibit the translation of a transfected reporter gene.