Rel-dependent decrease in the expression of ribosomal protein genes by inhibition of the respiratory electron transport chain in .

In this study, we demonstrated that both the expression of most ribosomal protein genes and the amount of ribosomes were decreased in the Δ mutant of , in which the major terminal oxidase ( cytochrome oxidase) of the respiratory electron transport chain (ETC) is inactivated, compared to those in the wild-type strain. Deletion of the gene encoding the major (p)ppGpp synthetase in the background of the Δ mutant restored the reduced expression of ribosomal protein genes, suggesting that inhibition of the respiratory ETC leads to the Rel-dependent stringent response (SR) in this bacterium. Both a decrease in the expression of ribosomal protein genes by overexpression of and the increased expression of in the Δ mutant relative to the wild-type strain support the Rel-dependent induction of SR in the Δ mutant.