Activates eif2ak2/pkr in the absence of double-stranded RNA (dsRNA), leading to phosphorylation of eif2s1/efi2-alpha and inhibition of translation and induction of apoptosis. Required for siRNA production by dicer1 and for subsequent siRNA-mediated post-transcriptional gene silencing. Does not seem to be required for processing of pre-miRNA to miRNA by dicer1 (By similarity). Homodimer. Interacts with dicer1 and eif2ak2/pkr. Also able to interact with dsRNA (By similarity). Associates with ribosomes. Expressed in brain, heart, kidney, liver, nerve and spleen. Belongs to the PRKRA family.