A MUTATION IN CYTOCHROME-OXIDASE SUBUNIT 2 RESTORES RESPIRATION OF THE MUTANT PET TS1402

The yeast PET1402/OXA1 gene encoding a 44.8-kDa protein is required fo r mitochondrial biogenesis. Substitution of Leu240 to serine in the pr otein results in an accumulation of the precursor form of the mitochon drially encoded subunit 2 of cytochrome oxidase (Cox2) and temperature -sensitive respiration. This temperature sensitivity can be suppressed by a mutation in the cox2 gene changing Ala189 of the Cox2 protein to proline. In the cox2-rs1402 double mutant respiration is restored wit hout removal of the Cox2 pre-sequence. The suppression suggests an int eraction of the Pet1402 protein with the cytochrome oxidase complex. A ntibodies raised against the predicted C-terminus and the tagged N-ter minus of the Pet1402 protein reacted with a 37-kDa polypeptide. This p rotein, present in the mitochondrial fraction, is localized within the inner membrane. The difference in size can be explained by the remova l of the predicted mitochondrial-targeting sequence from the Pet1402 p rotein. The mitochondrial localization of the protein points to a dire ct interaction with the cytochrome oxidase complex.