Fig. 4. GST–PKR and PKR (wt) show different sensitivities to the PKR inhibitors encoded by the vaccinia virus K3L and E3L genes. (A) Pseudosubstrate inhibition of PKR and GST–PKR. Yeast strain H1894 was transformed with a URA3 plasmid expressing GST–PKR (pC661), wild-type PKR (p1419), or the empty vector (pEMBLyex4) plus a LEU2 plasmid expressing the vaccinia virus K3L (pC365) or K3L-H47R (pC366) protein or the empty vector (pRS425). (B) Inhibition of PKR, but not GST–PKR, by the dsRNA-binding proteins E3L and PKR-ΔK. Yeast strain H1894 was transformed with a URA3 plasmid expressing GST–PKR (pC661) or wild-type PKR (p1419) plus a LEU2 plasmid expressing the vaccinia virus E3L (pC1315) or K3L-H47R (pC366) protein or the empty vector (pRS425), or a TRP1 plasmid expressing a truncated version of PKR lacking the kinase domain (PKR-ΔK, pC1316). All proteins in both (A) and (B) were expressed under the control of a yeast GAL-CYC1 promoter. Transformants were streaked on SGal minimal complete medium (synthetic minimal medium containing 10% galactose and supplemented with all amino acids), and the plates were incubated at 30°C for 8 days.