MECHANISM OF INTERFERON ACTION MOTIF-1 OF THE INTERFERON-INDUCED, RNA-DEPENDENT PROTEIN-KINASE (PKR) IS SUFFICIENT TO MEDIATE RNA-BINDING ACTIVITY

The interferon-induced P1/eIF-2α protein kinase cDNA, designated PKR, was expressed both in Escherichia coli and in transfected monkey COS cells. TrpE- PKR fusion proteins and PKR nonfusion proteins were examined for their RNA- binding activity by Northwestern blot analysis. PKR is a RNA-binding protein that possesses two copies of a highly conserved motif, R(I) and R(II), within the N-terminal region of the protein. Amino acid residues between 11 and 243 of PKR, which includes both copies of the R motif, displayed RNA-binding activity comparable to that of the full-length 551-amino-acid PKR protein. Analysis of substitution and deletion mutant PKR proteins revealed that motif R(I) was both necessary and sufficient for RNA-binding activity, whereas motif R(II) was not. Substitution of the highly conserved lysine at position 64 within the R(I) motif abolished RNA-binding activity, both of full-length PKR and the N-terminal 243-amino-acid truncated PKR. Finally, PKR substitution and deletion mutant cDNAs deficient for kinase function were expressed to much higher levels in transfected monkey cells than was the full-length wild-type PKR cDNA. © 1994 Academic Press, Inc.