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Pseudomonas aeruginosapathogenicity and its capability to adapt to multiple environments are dependent on the production of diverse virulence factors, controlled by the sophisticated quorum sensing (QS) network ofP. aeruginosa. To better understand the molecular mechanisms that underlie this adaptation we searched for novel key regulators of virulence factor production by screening a PA14 transposon mutant library for potential candidates acting downstream of the unique 2-alkyl-4-quinolone (AQ) QS system ofP. aeruginosa. We focused the work on a protein named HemK with high homology to PrmC ofEscherichia colidisplaying a similar enzymatic activity (therefore also referred to as PrmC). In this study, we demonstrate that PrmC is anS-adenosyl-l-methionine (AdoMet)-dependent methyltransferase of peptide chain release factors (RFs) essential for the expression of several virulence factors, such as pyocyanin, rhamnolipids and the type III-secreted toxin ExoT. Furthermore, the PA14_prmCmutant strain is unable to grow under anoxic conditions and has a significantly reduced pathogenicity in the infection modelGalleria mellonella. Along with transcriptomic and proteomic analyses, the presented data indicate that the methylation of RFs inP. aeruginosaseems to have a global effect on cellular processes related to the virulence of this nosocomial pathogen.