Abstract
Elongation factor G (EF-G) is a key protein in translational elongation. We have recently found that EF-G is inactivated via oxidation of two specific Cys residues and subsequent formation of an intramolecular disulfide bond in the cyanobacterium Synechocystis sp. PCC 6803. In the present study, we examined the role of EF-G (Slr1463) in the response of protein synthesis and PSII to strong light that gives rise to oxidative stress. When EF-G was overexpressed, the synthesis of the D1 protein de novo was enhanced under strong light, whereas the synthesis of almost all other proteins was suppressed. In this mutant, the level of another EF-G homolog Sll1098 decreased. When a modified EF-G (Slr1463) in which Cys105, a target of ROS, had been substituted by Ser was expressed together with wild-type EF-G, the synthesis of the D1 protein de novo was enhanced under strong light with no significant effects on the global synthesis of proteins. Moreover, the extent of photoinhibition of PSII in mutant cells was alleviated without any changes in the rate of photodamage to PSII. These observations suggest that the modified EF-G might enhance the repair of PSII during photoinhibition.
