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Intrinsic membrane sector (Fo) of H+-ATPase (FoF1) from Escherichia coli. Mutations in the alpha subunit give Fo with impaired proton translocation and F1 binding.

Mutant alleles for the alpha subunit of H+-translocating ATPase (FoF1) were cloned from Escherichia coli strains isolated in this laboratory. Determination of their DNA sequence revealed four nonsense mutations (KF3 and KF9, Gln-20----end; KF24, Trp-111----end; KF2, Trp-231----end; KF70, Gln-252----end) and one missense mutation (KF45, Pro-143----Ser). The membranes of all the mutants except strain KF9 (KF3) had 50-70% of ATPase activities of the wild-type. Unlike the F1-ATPase of the wild-type, those of the mutants were insensitive to dicyclohexylcarbodiimide and were easier to solubilize from membranes. As membranes of strain KF24 had F1-ATPase activity, these results suggest that at least a part of the F1-binding sites could be formed without a region between residues 111 and the carboxyl terminus of the alpha subunit. However, normal interactions between Fo and F1 require regions between residues 252 and 271 (carboxyl terminus) and in the vicinity of Pro-143. Membranes of strain KF45 were capable of forming a low ATP-driven H+ gradient, whereas other membranes were not. The possibility that the region between residues 252 and 271 is involved in H+ translocation is discussed.