Biochemical Analyses of oli1 and oli2 Gene Mutations Determining Primary Sequence Changes in Subunits 9 and 6 of Yeast ATP Synthase

Summary

The biochemical properties of mitochondrial mutants having primary sequence changes in either subunit 9 or 6 of yeast mitochondrial H⁺-ATPase have been examined. These mit ^- mutants display reduced ATPase activity which is uncoupled from proton translocation as indicated by insensitivity to inhibition by oligomycin. Several mutants with lesions in subunit 9, particularly those lacking C-terminal residues, assemble neither subunit 9 polypeptides nor subunits 8 and 6 to the H⁺- ATPase complex, as determined by immunoprecipitation. With the exception of one mutant forming a longer subunit 9 polypeptide, all mutants that fail to integrate subunit 9 into the complex show a pleiotropic effect in which there is a marked reduction in the synthesis of respiratory enzyme complexes, notably in cytochrome oxidase. Thus subunit 9 not only plays a key role in the assembly of the F₀-sector of H⁺-ATPase but it also has modulatory effects on the assembly of cytochrome oxidase. Mutations located in the hydrophilic loop region of subunit 9 have indicated a positive charge between residues 35 and 39 is required for H⁺-ATPase function but not for the assembly of the complex.