Phosphorylation of the α subunit of eukaryotic initiation factor 2 (eIF2α) is known to be an important translational control mechanism in all eukaryotes with the major exception of plants. Regulation of mammalian and yeast eIF2α activity is directly governed by specific phosphorylation on Ser-51. We now demonstrate that recombinant wheat wild-type (51S) but not mutant 51-Ala (51A) protein is phosphorylated by human PKR and yeast GCN2, which are defined eIF2α kinases. Further, only wheat wild-type eIF2α is a substrate for plant-encoded, double-stranded RNA-dependent kinase (pPKR) activity. Plant PKR and GCN2 phosphorylate recombinant yeast eIF2α 51S but not the 51A mutant demonstrating that pPKR has recognition site capability similar to established eIF2α kinases. A truncated version of wild-type wheat eIF2α containing 51S but not the KGYID motif is not phosphorylated by either hPKR or pPKR suggesting that this putative eIF2α kinase docking domain is essential for phosphorylation. Taken together, these results demonstrate the homology among eukaryotic eIF2α species and eIF2α kinases and support the presence of a plant eIF2α phosphorylation pathway.
Plant Molecular Biology – Springer Journals
Published: Oct 16, 2004
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