Genetic evidence for interaction between the a and b subunits of the F0 portion of the Escherichia coli proton translocating ATPase.

A mutation of the b subunit of the Escherichia coli proton translocating ATPase was previously described (Porter, A. C. G., Kumamoto, C., Aldape, K., and Simoni, R. D. (1985) J. Biol. Chem. 260, 8182-8187). This mutation, which causes substitution of aspartic acid for glycine at position 9 (basp9), results in loss of function of the ATPase complex. In this paper we describe the isolation and characterization of two mutations that partially suppress the effects of the basp9 alteration. The suppressor mutations cause amino acid substitutions at position 240 of the a subunit. Membranes derived from strains carrying a suppressor mutation and the basp9 mutation exhibited ATP-dependent proton translocating activity.