THE MOST CONSERVED NUCLEAR-ENCODED POLYPEPTIDE OF CYTOCHROME-C- OXIDASE IS THE PUTATIVE ZINC-BINDING SUBUNIT - PRIMARY STRUCTURE OF SUBUNIT-V FROM THE SLIME-MOLD DICTYOSTELIUM- DISCOIDEUM

A full-length 515 base pairs cDNA for cytochrome c oxidase subunit V of D. discoideum was isolated from a lambda gt11 expression library. The encoded polypeptide, whose identity was confirmed by partial protein sequencing, is 119 amino acids long (Mr = 13,352) and does not contain a cleavable presequence. The protein, which is homologous to human subunit Vb and yeast subunit IV, exhibits the highest degree of sequence conservation found among nuclear-encoded subunits of cytochrome c oxidase from distantly related organisms. All the invariant residues are clustered in two regions of the C-terminus which include the putative amino acids involved in the coordination of the Zn ion tightly associated to eukaryotic oxidase.