Methylation at position 32 of tRNA catalyzed by TrmJ alters oxidative stress response in Pseudomonas aeruginosa

Bacteria respond to environmental stresses using a variety of signaling and gene expression pathways, with translational mechanisms being the least well understood. Here, we identified a tRNA methyltransferase in Pseudomonas aeruginosa PA14, trmJ, which confers resistance to oxidative stress. Analysis of tRNA from a trmJ mutant revealed that TrmJ catalyzes formation of Cm, Um, and, unexpectedly, Am. Defined in vitro analyses revealed that tRNAMet(CAU) and tRNATrp(CCA) are substrates for Cm formation, tRNAGln(UUG), tRNAPro(UGG), tRNAPro(CGG) and tRNAHis(GUG) for Um, and tRNAPro(GGG) for Am. tRNASer(UGA), previously observed as a TrmJ substrate in Escherichia coli, was not modified by PA14 TrmJ. Position 32 was confirmed as the TrmJ target for Am in tRNAPro(GGG) and Um in tRNAGln(UUG) by mass spectrometric analysis. Crystal structures of the free catalytic N-terminal domain of TrmJ show a 2-fold symmetrical dimer with an active site located at the interface between the monomers and a flexible basic loop positioned to bind tRNA, with conformational changes upon binding of the SAM-analog sinefungin. The loss of TrmJ rendered PA14 sensitive to H2O2 exposure, with reduced expression of oxyR-recG, katB-ankB, and katE These results reveal that TrmJ is a tRNA:Cm32/Um32/Am32 methyltransferase involved in translational fidelity and the oxidative stress response.