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 F-0 sector of the Escherichia coli F1F0 ATPase is dependent upon the level of atpE gene expression. F-0 was purified from cells carrying plasmids encoding the F-0 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 F-0. Immunoblot quantitation of the amounts of b and c subunits in F1F0 precipitated by anti-F-1 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. (C) 1995 Academic Press, Inc.