Intergenic suppression in a β subunit mutant with defective assembly in Escherichia coli F1ATPase

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Abstract
Substitution of Leu‐40 by Pro in the β subunit (βL40P) of Escherichia coli F1‐ATPase caused a decrease in the amount of the α and β subunits on the membranes. A revertant strain, Re50, carrying no suppression mutations in the uncD gene encoding the β subunit, was isolated from the βL40P mutant. The uncA gene from this revertant was amplified by PCR, and cloned into an expression plasmid. The expression plasmid carrying the uncA gene from the revertant was used for genetic suppression assays. The suppression mutation in Re50 was in the α subunit, and it recovered the assembly of the α and β subunits into the F1F0 complex and the ATPase activity to 50% that of the wild type. In Re50, Leu‐111 was substituted by Gln in the α subunit. These results suggest that the regions including Leu‐40 in the β subunit and Leu‐111 in the α subunit are located close together and interact with each other, either directly or indirectly.