Mode of action of the cloacin DF13-immunity protein.

1. Cells of Enterobacter cloacae harbouring the bacteriocinogenic factor Clo DF13 produce an immunity protein which inbhbits the in vitro activity of cloacin DF13. The amino acid composition of purified immunity protein was determined. 2. Experiments about the protection of ribosomes against cloacin DF13 in the presence of the immunity protein show that one molecule of immunity protein neutralized the activity of one molecule cloacin. 3. Direct and specific interaction of cloacin DF13 with the immunity protein has been demonstrated by the analysis of mixtures of both proteins on polyacrylamide gels and by changes in the fluorescence response of cloacin DF13-bound 1-anilinonaphthalene-8-sulfonate in the presence of immunity protein.