Localization of unassembled subunits of the mitochondrial ATPase in an assembly-defective yeast nuclear mutant.

The yeast nuclear mutant, pet 936, has previously been shown to be defective in the assembly of a functional mitochondrial ATPase (Todd, R. D., McAda, P. C., and Douglas, M. G. (1979) J. Biol. Chem. 254, 11134-11141). In the present report, trypsin degradation and subunit-specific antibody binding have been used to localize subunits 1, 2, and 3 external to or associated with the outer aspect of the inner mitochondrial membrane in the mutant strain. A similar population of unassembled subunits was found in the parental strain as well. Isotope dilution experiments are compatible with those unassembled subunits being normal intermediates in the assembly pathway of the ATPase complex which are blocked from transport across the inner mitochondrial membrane in the mutant, pet 936.