Energy coupling factor as target of colicin K: characterization of a colicin K-insensitive ecf mutant of Escherichia coli.

We isolated a colicin K-insensitive energy uncoupled mutant of Escherichia coli. This mutant was presumed to be an ecf mutant as evidenced by its similarity to a known ecf mutant (M. A. Lieberman and J.-S. Hong, 1974) with respect to the mutational site, reversion pattern, and defects in transport and growth. The mutation conferring the colicin K-insensitivity resided in the ecf gene as the majority of the secondary mutations overcoming the ecf phenotype reverted the colicin K-insensitive phenotype to colicin K-sensitive. The insensitivity of the mutant to colicin K was not due to either a defect in adsorption or to a lack of the energized membrane state. The defect was most probably due to the inability of colicin K molecules to interact with their target. Our previous studies concerning the role of the ecf gene product in energy coupling to active transport and oxidative phosphorylation support the contention that the ECF protein is itself the direct target of colicin K.