FIG. 2.

Rationale for a selection scheme to identify mutants defective in protein export from the mitochondrial matrix. An arg8 strain containing the COX2::ARG8^m chimeric gene in its mtDNA (SH45B) exhibits an Arg⁻ growth phenotype due to export of the Arg8^mp moiety, which can function only in the matrix (Fig. 1). The strain can respire (Pet⁺) due to the normal translocation of Cox2p through the inner membrane followed by proteolytic removal of the Arg8^mp moiety (not shown). An Arg⁺ growth phenotype could result from a defect in export that results in accumulation of the Arg8^mp moiety in the matrix. If the defect is severe enough, it will also prevent the export of Cox2p domains to the IMS and the assembly of cytochrome oxidase, producing a Pet⁻ phenotype.