Oxidation of elongation factor G inhibits the synthesis of the D1 protein of photosystem II

Oxidative stress inhibits the repair of photodamaged photosystem II (PSII). This inhibition is due initially to the suppression, by reactive oxygen species (ROS), of the synthesis de novo of proteins that are required for the repair of PSII, such as the D1 protein, at the level of translational elongation. To investigate in vitro the mechanisms whereby ROS inhibit translational elongation, we developed a translation system in vitro from the cyanobacterium Synechocystis sp. PCC 6803. The synthesis of the D1 protein in vitro was inhibited by exogenous H₂O₂. However, the addition of reduced forms of elongation factor G (EF-G), which is known to be particularly sensitive to oxidation, was able to reverse the inhibition of translation. By contrast, the oxidized forms of EF-G failed to restore translational activity. Furthermore, the overexpression of EF-G of Synechocystis in another cyanobacterium Synechococcus sp. PCC 7942 increased the tolerance of cells to H₂O₂ in terms of protein synthesis. These observations suggest that EF-G might be the primary target, within the translational machinery, of inhibition by ROS.