PKR: a new name and new roles

The double-stranded RNA (dsRNA)-activated protein kinase, now called PKR, was first discovered by virtue of its ability to phosphorylate translation initiation factor elF-2 and inhibit its activity. Recent studies have shown that expression of inactive mutants of PKR in cultured cells causes them to acquire characteristics typical of transformed cells. These and other findings indicate that PKR plays a role in the normal control of cell growth and differentiation. It seems likely that, in addition to elF-2, PKR has other substrates including the protein I-κB, which regulates the transcription of certain genes. Indeed, it now seems likely that PKR mediates the regulation of selected genes by dsRNA.