Structure and regulation of eukaryotic initiation factor eIF-2. Sequence of the site in the alpha subunit phosphorylated by the haem-controlled repressor and by the double-stranded RNA-activated inhibitor

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Abstract
Eukaryotic protein synthesis initiation factor 2 (eIF-2) can be phosphorylated on its α subunit by two well-characterised protein kinases, termed the haem-controlled repressor (HCR) and the double-stranded RNA-activated inhibitor (dsl). Phosphorylation of eIF-2 by these kinases is thought to be important in the regulation of peptide-chain initiation. We report the location of the serine residue in the α subunit, which is phosphorylated by both these enzymes. Limited tryptic digestion and subsequent cyanogen bromide treatment of rat liver eIF-2 phosphorylated by HCR yielded one major phosphopeptide. This peptide had the sequence The same major phosphopeptide was obtained from rabbit reticulocyte eIF-2 phosphorylated by HCR or dsI as judged by its behaviour on two-dimensional mapping and reverse-phase chromatography. In all cases the phosphorylated residue was found to be serine-7, and not serine-4, of the above sequence as determined from sequence analysis and by subdigestion of the peptide with Staphylococcus aureus V8 proteinase.

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