Interaction of colicins with bacterial cells. I. Studies with radioactive colicins.

Maeda, Akio (Department of Genetics, University of Wisconsin, Madison), and Masayasu Nomura. Interaction of colicins with bacterial cells. I. Studies with radioactive colicins. J. Bacteriol. 91:685-694. 1966.-By use of a preparation of radioactive colicin E2, the following conclusions, which had been obtained previously from indirect experiments, were tested directly: (i) colicin stays at the receptor site on the cell and acts from there; (ii) colicins E2 and E3 share the same receptor, although their mode of action is entirely different; (iii) colicinogenic cells adsorb homologous colicin, although they are resistant to that colicin. Our experimental results confirmed the above conclusions. When sensitive cells of Escherichia coli K-12 pretreated with radioactive E2 were disrupted with a French pressure cell, and fractionated by differential centrifugation, it was found that most of the radioactivity stayed with the cell envelope fraction. Trypsin removed a major part of radioactivity from cells pretreated with radioactive E2, as was expected from the previous experiments on trypsin reversal of colicin action. Furthermore, it was shown that the trypsin treatment causes a recovery of the capacity of E2-pretreated cells to adsorb further colicin E2. When cells were first treated with various amounts of nonradioactive E3, and then treated with radioactive E2, the amount of radioactive E2 adsorbed was found to be inversely related to the amount of nonradioactive E3 adsorbed first. It was also shown that E2-colicinogenic cells adsorb radioactive E2, and yet are resistant to this colicin.