Potential EF-P modification pathways. A- Mechanism in which YjeA acts first on free lysine (Lys) and attaches it to EF-P Lys34 which is then modified on EF-P into β-lysine by YjeK. B- Mechanism in which YjeK acts first to modify free lysine into β-lysine which is subsequently activated by YjeA and attached to EF-P lysine 34. EF-P N-terminal loop is indicated in yellow, Lys 34 is indicated in red, the modification appear on light brown and the AMP generated by YjeA during the activation of the Lys residue appear in blue. Potential and known substrates and cofactors of each enzyme are indicated.