Deletions in hydrophilic domains of subunit a from the Escherichia coli F1F0-ATP synthase interfere with membrane insertion or F0 assembly.

The a subunit is a membrane component of the F1F0-ATP synthase from Escherichia coli. Regions of a which appear important for membrane insertion or F0 assembly have been identified by analysis of both deletion mutants and fusion proteins which link the mutant a subunits to alkaline phosphatase. This analysis suggests the hydrophilic, amino-terminal domain of a is required for proper membrane targeting and/or insertion of the nascent polypeptide. In addition, the subcellular fractionation of four different a subunit-beta-galactosidase fusion proteins suggests this domain is localized to the periplasm, in agreement with a proposed topological model of the protein (Lewis, M.J., Chang, J.A., and Simoni, R.D. (1990) J. Biol. Chem. 265, 10541-10550). Deletions within the next three putative loops of a appear to have no significant effect on membrane targeting or insertion. Rather, they seem to interfere with the subsequent assembly of a functional enzyme.