Microcin J25 (MccJ25) cyclic 21 aa peptide, derived from a precursor of 58 aas. The Ile13 residue of microcin J25 is essential for recognition by the receptor FhuA, but not by the inner membrane transporter SbmA (Socias et al., 2009). It inhibits transcription by binding deep within RNAP secondary channel, where it sterically blocks the folding of the trigger loop, which is essential for efficient catalysis (Mukhopadhyay et al. 2004; Braffman et al. 2019). It also acts on the cytoplasmic membrane of Salmonella newport, producing alteration of membrane permeability and subsequent gradient dissipation, which inhibits several processes essential for cell viability, such as oxygen consumption (Rintoul et al. 2001).