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'. Homodimer. Belongs to the class-II aminoacyl-tRNA synthetase family. EpmA subfamily.