Adenosine 5'-triphosphate-linked transhydrogenase in cytoplasmic membranes of colicin-treated and untreated Escherichia coli

Cloning of colicin E1 tolerant tolC (mtcB) gene of Escherichia coli K12 and identification of its gene product

A mutation in the tolC(mtcB) gene of Escherichia coli K12 results in increased sensitivity to sodium dodecylsulfate (SDS), sodium deoxycholate, basic dyes, mitomycin C, and bleomycin, and makes the cell tolerant to the killing action of colicin E1. From lysogens with lambda cI857S7 integrated at a secondary attachment site, a transducing phage (lambda dtolC+) that transduces a tolC recipient to SDS resistance was isolated. A recombinant DNA molecule was constructed in vitro from plasmid pBR322 as a vector, and an EcoRI-BamHI fragment of lambda tolC+ DNA. The resulting plasmid, designated pOK1, was 5.6 megadaltons (Md). The tolC bacteria transformed with plasmid pOK1 restored the TolC+ phenotype with regard to mitomycin C, SDS, and colicin E1 sensitivities. A plasmid with an amber mutation in the tolC gene, designated pOK18, was isolated by the same procedure used for the isolation of pOK1. The plasmid had a molecular weight of 5.6 Md and produced the same size of DNA fragments as the tolC+ plasmid, pOK1, after digestion with the indicated restriction enzymes. The plasmid, pOK18, conferred the TolC+ phenotype when introduced into a tolC strain in the presence of, but not the absence of, an amber suppressor. Plasmid-specified polypeptides were determined by using maxicells of strains uvrA recAsup+ and uvrA recA tyrT, containing each plasmid. Three additional proteins of 54,000 (54K), 29K, and 27K were produced in maxicells containing pOK1. These three proteins were synthesized in maxicells of the uvrA recA tyrT strain carrying pOK18, whereas synthesis of the 54K protein by pOK18 did not take place in maxicells of the uvrA recA sup+ strain, although the other two proteins were produced in normal amounts. From these results we concluded that the product of the tolC gene is a protein with a molecular weight of 54K.

Interaction of 125I-labeled colicin E1 with Escherichia coli

Colicin E1 protein was labeled with (125)I to specific activities of up to 2 x 10(8) cpm/mg of protein and with no loss of the colicin biological activity. The labeled colicin bound to colicin E1-sensitive, tolerant, and immune E1-colicinogenic Escherichia coli. An E. coli mutant resistant to colicin E1 exhibited a much lower colicin-binding capacity. The average number of bound colicin molecules per sensitive cell increased as a function of the colicin concentration in the colicin cell interaction mixture and continued to increase even after loss of viability of the entire culture. Up to 2,400 colicin E1 molecules bound per cell, but saturation was not reached. Binding kinetics showed that maximum binding occurred within 2 to 5 min of colicin addition. Survival and binding assays indicated that one colicin killing unit corresponded to an average of about 100 colicin molecules bound per bacterial cell. This number, however, decreased to about 8 in more extensively washed cells. Trypsin digestion of the colicin-treated cells removed the majority of the cell-bound colicin, but in general provided little rescue from colicin killing. At low colicin concentrations, a linear relationship existed between survival and the number of trypsin-inaccessible colicin molecules. Under these circumstances and in agreement with single-hit kinetics, the relationship between the number of colicin killing units and the number of trypsin-inaccessible colicin molecules was close to 1. After trypsin digestion, cells that were nearly saturated with colicin retained about 200 trypsin-inaccessible colicin molecules per cell. The trypsin-inaccessible colicin might represent those colicin molecules that bound to the specific E colicin receptors of E. coli cells.