The Effects of anatpERibosome-Binding Site Mutation on the Stoichiometry of the c Subunit in the F1F0ATPase ofEscherichia coli

We tested the hypothesis that the stoichiometry of the c subunit in the F0sector of the Escherichia coli F1F0ATPase is dependent upon the level of atpE gene expression. F0was purified from cells carrying plasmids encoding the F0subunits with and without a ribosome-binding site mutation preceding atpE, the gene which codes for the c subunit. Subunit-specific antibodies were used to quantitate the relative amounts of the b and c subunits. The decreased expression of atpE resulted in a significantly decreased amount of the c subunit in the purified F0. Immunoblot quantitation of the amounts of b and c subunits in F1F0precipitated by anti-F1antiserum also showed that the mutation produced significant differences in the stoichiometry of subunit c. The amount of c subunit assembled into the F1F0synthesized from a plasmid carrying the atpE ribosome binding site mutation was 2–5 times less than the amount found in the F1F0synthesized from a wild-type plasmid. Therefore, the stoichiometry of the c subunit assembled into the F1F0complex appears to be variable, depending on the expression of atpE.