On the functions of the yeast COX10 and COX11 gene products.

COX10 and COX11 are nuclear genes of Saccharomyces cerevisiae whose products are localized in mitochondria and are required for the synthesis of cytochrome oxidase. Genes homologous to COX10 are present in at least four different bacterial cytochrome oxidase operons. The bacterial gene, termed cyoE, has recently been proposed to code for a farnesyl transferase that converts protoheme to heme O (Saiki et al. (1992), Biochem. Biophys. Res. Commun. 189, 1491-1497). In this communication we report that the COX10 protein, like the product of cyoE is needed for heme A synthesis. Analyses of the heme constituents in a cox11 mutant indicate the absence of heme A and presence of a novel heme with chromatographic properties indistinguishable from those of heme O. This evidence suggests that the COX11 protein may be another heme A biosynthetic enzyme involved in forming the formyl group at position 8 of the porphyrin ring.