The complete amino acid sequences of subunits VII and VIIa from yeast cytochrome c oxidase are reported. Subunits VII and VIIa are 57 residues (Mr = 6603) and 54 residues (Mr = 6303) in length, respectively. Both polypeptides are amphiphilic, have an internal hydrophobic section and hydrophilic NH2 and COOH termini, and terminate at their COOH termini with a basic amino acid. This structural motif is similar to that possessed by subunit VIII of yeast cytochrome c oxidase. All three polypeptides have hydrophobic sections which are long enough to span the inner membrane; all three polypeptides lack methionine at their NH2 termini; and all three polypeptides have COOH termini which could result from proteolysis by a protease with trypsin or cathepsin B-like activity. These observations raise the interesting possibility that subunits VII, VIIa, and VIII are transmembranous polypeptides which are processed at both their NH2 and COOH termini during their biogenesis.