Phosphorylation of only serine-51 in protein synthesis initiation factor-2 is associated with inhibition of peptide-chain initiation in reticulocyte lysates.

We have examined the phosphorylation of the alpha-subunit of initiation factor-2 (eIF-2 alpha) in reticulocyte lysates in which translational shut-off was induced by haem-deficiency or by double-stranded RNA. To maximise the phosphorylation of eIF-2 alpha, lysates were supplemented with the broad spectrum phosphatase inhibitor microcystin. Under all conditions tested, serine-51 was the only residue to become labelled. This is consistent with the observation of only two species of eIF-2 alpha in isoelectric focusing/immunoblotting analyses of lysates treated as described above.