EVIDENCE THAT THE IMMUNITY PROTEIN INACTIVATES COLICIN-5 IMMEDIATELY PRIOR TO THE FORMATION OF THE TRANSMEMBRANE CHANNEL

Determination and analysis of the nucleotide sequences of the activity , immunity, and lysis genes of colicin 5 assigned colicin 5 to the sub class of pore-forming colicins to which colicins 10, E1, Ia, Ib, and K belong, Mutational analysis of colicin 5 and exchange of DNA fragment s between the most closely related colicins, colicins 5 and 10, and be tween their immunity proteins localized the regions that determine the reaction specificity between colicin 5 and its immunity protein to re sidues 405 to 424 of colicin 5, the region corresponding to the amphip hilic alpha-helix 6 of the similar colicins E1 and Ia, The specificity -conferring residues 55 to 58 and 68 to 75 of the immunity protein wer e localized in the cytoplasmic loop and the inner leaflet of the cytop lasmic membrane, The localization of the reactive regions of the immun ity protein and the colicin close to the inner side of the cytoplasmic membrane suggests that the immunity protein inactivates colicin 5 sho rtly before the lethal colicin pores in the cytoplasmic membrane are o pened.