Identification of functional domains in Atp11p. Protein required for assembly of the mitochondrial F1-ATPase in yeast.

The Atp11p protein of Saccharomyces cerevisiae is required for proper assembly of the F1 component of the mitochondrial ATP synthase. The mutant atp11 genes were cloned and sequenced from 12 yeast strains, which are respiratory-deficient due to a defect in Atp11p function. Four of the mutations mapped to the mitochondrial targeting domain (amino-terminal 39 amino acids) of Atp11p. All the genetic lesions found in the mature protein sequence were shown to be nonsense mutations. This result is consistent with the idea that Atp11p activity is provided, principally, by the overall structure of a functional domain, and not by specific amino acid residues in a localized active site. Amino-terminal (Edman) sequence analysis of fragments derived from limited proteolysis of purified Atp11p, and in vivo functional characterization of deletion mutants, were employed to locate the position of the active region in the protein. Three domains, separated by proline-rich sequences, were identified in the mature protein. The active domain of Atp11p was mapped to the sequence between Phe-120 and Asn-174. The domains proximal (Glu-40 through Ser-109) and distal (Arg-183 through Asn-318) to the active region were found to be important for the protein stability inside mitochondria.