- The interferon-induced double-stranded RNA-activated protein kinase PKR will phosphorylate serine, threonine, or tyrosine at residue 51 in eukaryotic initiation factor 2alpha. Lu, J., O'Hara, E.B., Trieselmann, B.A., Romano, P.R., Dever, T.E. J. Biol. Chem. (1999)