Isolation and characterization of a mutant colicin E2.

Escherichia coli K-12 colicinogenic for Col E2 yielded a mutant, SK95, that carries a nonsense mutation in the colicin structural gene. A derivative of SK95 that carries an as yet unidentified suppressor mutation produces a colicin E2 that is temperature sensitive (TS). This mutant colicin kills sensitive cells at low temperature but not at high temperature; the colicin adsorbs to cells at high temperature but does not kill them unless the temperature is lowered. Unlike normal colicin E2, which adsorbs rapidly to cells, TS colicin E2 adsorbs slowly over a period of several hours. The biochemical target of colicin E2 is deoxyribonucleic acid (DNA). When acid solubilization of DNA was compared in cells treated with either TS or normal colicin E2, striking differences were observed. Cell killing and acid solubilization of DNA by colicin E2 were shown to be separable events under certain conditions. The results are discussed in relation to the mechanism of action of colicin E2.