With EpmB is involved in the beta-lysylation step of the post-translational modification of translation elongation factor P (EF-P) on 'Lys-34'. Catalyzes the ATP-dependent activation of (R)-beta-lysine produced by EpmB, forming a lysyl-adenylate, from which the beta-lysyl moiety is then transferred to the epsilon-amino group of EF-P 'Lys-34' (Probable). Can also use L-alpha-lysine as a substrate, but probably with lower efficiency. Cannot aminoacylate tRNA(Lys) with lysine. Homodimer. Mutants have a reduced pyruvate oxidase activity and a reduced growth rate, and are highly attenuated for virulence in mouse models of infection. Salmonella epmA and epmB mutants share extensive phenotypic pleiotropy, including an increased ability to respire under nutrient-limiting conditions, hypersusceptibility to a variety of diverse growth inhibitors, and altered expression of multiple proteins, including several encoded on the SPI-1 pathogenicity island. Belongs to the class-II aminoacyl-tRNA synthetase family. EpmA subfamily.