Deletion of the ribosomal protein gene rpmJ activates zntA transcription through a translation-dependent mechanism in Escherichia coli

Bacteria tightly regulate intracellular zinc homeostasis by coordinating zinc uptake and efflux systems. We previously showed that deletion of the ribosomal protein gene rpmJ confers zinc resistance in Escherichia coli in a manner dependent on the zinc efflux transporter zntA. Here, we analyzed the effect of rpmJ deficiency on zntA expression. Under zinc excess conditions, zntA mRNA levels were markedly higher in the rpmJ mutant than in the wild-type strain. Enhanced zntA expression required the native zntA promoter, the native Shine-Dalgarno sequence, and the N-terminal coding region of zntA, indicating that translation initiated from the native Shine-Dalgarno sequence and extending through the N-terminal coding region is required for enhanced transcription initiation from the native zntA promoter. Furthermore, ectopic expression of ykgO, a paralog of rpmJ that is known to replace RpmJ on the ribosome under zinc-limited conditions, abolished the increased zntA expression and zinc resistance conferred by rpmJ deletion. Collectively, these findings suggest that ribosomes lacking RpmJ or YkgO promote transcription initiation from the native zntA promoter through translation of zntA mRNA.