Use of lambda unc transducing bacteriophages in genetic and biochemical characterization of H+-ATPase mutants of Escherichia coli

Abstract

The eight subunits of the H+-ATPase of Escherichia coli are coded by the genes of the unc operon, which maps between bglB and asnA. A collection of unc mutations were transferred via P1 transduction into a strain in which lambda cI857 S7 was inserted into bglB. The lambda phage was induced, and asnA+ transducing phage that carried unc were selected. Transducing phage carrying mutations in the uncA, B, D, E, and F genes were used for complementation analysis with a collection of unc mutants, including mutants which had been reported previously but not genetically characterized. Some mutations gave a simple complementation pattern, indicating a single defective gene, whereas other mutations gave more complex patterns. Two mutants (uncE105 and uncE107) altered in the proteolipid (omega) subunit of F0 were not complemented by any of the lambda unc phage, even though both mutants had a fully functional F1 ATPase and therefore normal A and D genes. Hence, only limited conclusions can be drawn from genetic complementation alone, since it cannot distinguish normal from abnormal genes in certain classes of unc mutants. The lambda unc phage proved to be essential in characterizing several mutants defective in F0-mediated H+ translocation. The unc gene products were overproduced by heat induction of the lysogenized lambda unc phage to determine whether all the F0 subunits were in the membrane. Two mutants that gave a simple complementation pattern, indicative of one defective gene, did not assemble a three-subunit F0. The uncB108 mutant was shown to lack the chi subunit of F0 but to retain psi and omega. Trace amounts of an altered omega subunit and normal amounts of chi and psi were found in the uncE106 mutant. A substitution of aspartate for glycine at residue 58 of the protein was determined by DNA sequence analysis of the uncE gene cloned from the lambda uncE106 phage DNA. One of the omega-defective, noncomplementing mutants (uncE107) was shown to retain all three F0 subunits. The uncE gene from this mutant was also sequenced to confirm an asparagine-for-aspartate substitution at position 61 (the dicyclohexylcarbodiimide-binding site) of the omega subunit.