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Effects of Colicin E3 on Bacterial Ribosomes

M. Nomura, J. Sidikaro, K. Jakes, N. Zinder


Studies of the relation of the structure to function of ribosomes can be approached in several ways. For example, the role of the various components of ribosomes can be directly analyzed by reconstitution experiments (see Nomura and Held, this volume). Another approach is modification of these components in situ by the use of specific reagents. In this article, the inactivation of ribosomes by colicin E3 will be discussed in the light of our developing understanding of its specific mode of action.

The bacteriocins are bactericidal substances which are synthesized by certain strains of bacteria and have killing activity against some other strains of the same or closely related species. Colicins are one class of such bacteriocins. Several colicins have been studied with respect to their chemical nature, genetic determinants, and mode of action. Colicins are proteins and are produced by cells which carry a plasmid called colicinogenic factor or Col factor. The presence of a Col factor in a cell confers on it both the ability to produce the colicin as well as immunity against the corresponding colicin (Fredericq 1958). In killing sensitive cells, colicins first adsorb to specific receptors on the cell surface. Colicin E3 shares its adsorption specificity with colicins E1 and E2 and with bacteriophage BF23. Cells which lack such receptors are resistant to the colicins. For example, most of the mutants of E. coli that are resistant to BF23 are also resistant to colicins E1, E2, and E3; the resistance is due to...

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