Overexpression of Ribosomal Proteins Leads to Zn Resistance in Escherichia coli

Knockout of ribosomal protein bL36 (RpmJ) leads to Zn resistance in Escherichia coli, and the expression of ribosomal protein genes other than RpmJ increase in the rpmJ-knockout strain. In this study, we examined whether the overexpression of ribosomal proteins causes Zn resistance using an E. coli overexpression gene library (ASKA clone library). The overexpression of 48 of the 54 ribosomal proteins led to Zn resistance. However, the overexpression of proteins other than ribosomal proteins did not lead to Zn resistance, suggesting that Zn resistance is a phenomenon specific to the overexpression of ribosomal proteins. In addition, the overexpression of ribosomal proteins did not lead to resistance to metal ions other than Zn (Cu2+, Ni2+, Mn2+, and Ag+), suggesting a Zn-specific resistance mechanism. Deletion of ZntA, a Zn efflux pump, resulted in the loss of Zn resistance in a ribosomal protein-overexpressing strain. Deletion of Lon protease, which is responsible for degrading misfolded proteins, in a ribosomal protein-overexpressing strain resulted in the accumulation of overexpressed ribosomal proteins and loss of Zn resistance. These results suggest that the overexpression of ribosomal proteins leads to Zn resistance in E. coli via ZntA and Lon protease. ImportanceThe ribosome is a complex comprising ribosomal RNAs and more than 50 types of ribosomal proteins. Ribosomal proteins play an important role in ribosomal function responsible for protein translation; however, their involvement in other cellular processes is not fully understood. Based on the finding that ribosomal protein expression increases in a Zn-resistant E. coli mutant, we analyzed 54 ribosomal proteins and found that the overexpression of 48 ribosomal proteins led to Zn resistance. This finding suggests a role for ribosomal proteins in resistance to zinc stress.