The CFTR inhibitory factor (Cif) is a protein virulence factor secreted by the Gram-negative bacteria Pseudomonas aeruginosa and Acinetobacter nosocomialis. Discovered at Dartmouth Medical School, Cif is able to alter the trafficking of select ABC transporters in eukaryotic epithelial cells, such as the cystic fibrosis transmembrane conductance regulator (CFTR), and P-glycoprotein by interfering with the host deubiquitinating machinery. By promoting the ubiquitin-mediated degradation of CFTR, Cif is able to phenocopy cystic fibrosis at the cellular level. The cif gene is transcribed as part of a 3 gene operon, whose expression is negatively regulated by CifR, a TetR family repressor.