Yeast mitochondrial Sco1p is required for the formation of a functional cytochrome c oxidase (COX). It was suggested that Sco1p aids copper delivery to the catalytic center of COX. Here we show by affinity chromatography and coimmunoprecipitation that Sco1p interacts with subunit Cox2p. In addition we provide evidence that Sco1p can form homomeric complexes. Both homomer formation and binding of Cox2p are neither dependent on the presence of copper nor affected by mutations of His-239, Cys-148 or Cys-152. These amino acids, which are conserved among the members of the Sco1p family, have been suggested to act in the reduction of the cysteines in the copper binding center of Cox2p and are discussed as ligands for copper. ß

The Gpr1 protein of the ascomycetous yeast Yarrowia lipolytica belongs to the poorly characterized Gpr1/Fun34/YaaH protein family, members of which have thus far only been found in prokaryotes and lower eukaryotes. Trans-dominant mutations in the GPR1 gene result in acetic acid sensitivity of cells at low pH. Moreover, Gpr1p is subjected to phosphorylation at serine-37 in a carbon source-dependent manner. Here we show that several mutations within the ORFs of the GPR1 orthologues of Saccharomyces cerevisiae, YCR010c (ATO1) and YNR002c (ATO2), also trans-dominantly induce acetic acid hypersensitivity in this yeast. We demonstrate that the C-termini of mutated Gpr1p, Ycr010cp and Ynr002cp are necessary for the triggering of acetic acid sensitivity. Phosphorylation of Y. lipolytica Gpr1p was also affected by several mutations. Data further suggest that Gpr1p exists in an oligomeric state.

No abstract