Characterization of a mutation in the cloacin structural gene causing a reduced uptake of cloacin DF13 by susceptible cells

Abstract The plasmids CloDF13-clp03 and CloDF13-clp21, obtained after nitrosoguanidine mutagenesis of pCloDF13 (Andreoli, P.M. and Nijkamp, H.J.J. (1976) Mol. Gen. Genet. 144, 159–170), encode mutant bacteriocin molecules with a reduced ability to penetrate susceptible cells (Gaastra, W., Oudega, B. and De Graaf, F.K. (1978) Biochim. Biophys. Acta 540, 301–312). DNA sequence analysis revealed that both the genes encoding the mutant bacteriocin molecules had a point-mutation which resulted in the replacement of proline⁵⁴ by serine in the amino-terminal domain of the cloacin, involved in translocation. This alteration had no detectable effect on the predicted secondary structure of the proteins or on the interaction with various monoclonal antibodies. Susceptible cells with a relatively low number of receptor proteins were not killed by the bacteriocins or were less susceptible, but Escherichia coli cells with a relatively high number of efficient and functional receptor proteins were efficiently killed. Immunoblotting experiments with the latter type of cells showed that cloacin-clp03, like native cloacin DF13, was fragmented during uptake by the cells, but at a somewhat slower rate.