Purification and Properties of Colicin E3 Immunity Protein

A which inhibits the in vitro effects of colicin E3 (E3) was purified from cells colicinogenic for E3 by chromatography on DEAE-Sephadex and Sephadex G-75. This protein could be isolated both from uninduced and mitomycin C-induced colicinogenic cells, but not from cells lacking the Col E3 factor. It is a highly acidic of molecular weight about 10,000. At concentrations approximately equimolar to that of the colicin, it completely prevents colicin E3 from inhibiting in vitro synthesis. Even in vast molar excess, however, it has no effect on the in vivo killing of sensitive cells by the colicin. Experiments to investigate the effect of immunity on inhibition of in vitro synthesis by colicin E3 are consistent with a model in which immunity interacts with the colicin to prevent its destruction of ribosomes. Preliminary direct binding experiments have failed to reveal interaction of immunity either with colicin or with ribosomes. However, highly purified colicin contains a component which co-migrates with immunity on sodium dodecyl sulfate-acrylamide-urea gels.