The effects of an atpE ribosome-binding site mutation on the stoichiometry of the c subunit in the F1F0 ATPase of Escherichia coli.

We tested the hypothesis that the stoichiometry of the c subunit in the F0 sector of the Escherichia coli F1F0 ATPase is dependent upon the level of atpE gene expression. F0 was purified from cells carrying plasmids encoding the F0 subunits 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 F1F0 precipitated by anti-F1 antiserum also showed that the mutation produced significant differences in the stoichiometry of subunit c. The amount of c subunit assembled into the F1F0 synthesized from a plasmid carrying the atpE ribosome binding site mutation was 2-5 times less than the amount found in the F1F0 synthesized from a wild-type plasmid. Therefore, the stoichiometry of the c subunit assembled into the F1F0 complex appears to be variable, depending on the expression of atpE.