Cytochrome b-deficiency in a mitochondrial muc1muc2 recombinant of Saccharomyces cerevisiae

Summary Cytochrome b-deficient muc1muc2 recombinants of Saccharomyces cerevisiae carrying two specific mitochondrial mucidin-resistant mutations were not able to grow on nonfermentable substrates with the exception of lactate. Crosses of the selected muc1muc2 recombinant strain H331 with different box mutants yielded progenies of mucidin-resistant colonies in a pattern which demonstrates the double mutation origin of the recombinant cells.Only 20% of the wild type cytochrome b content was spectrally detected in the muc1muc2 recombinant, which, however, contained normal amounts of cytochromes c and a when grown under derepressing conditions. The respiratory activity of mitochondria isolated from the muc1muc2 recombinant was limited at the level of cytochrome b and was specifically resistant to high concentrations of mucidin. Electrophoretic analysis of the radioactive products of mitochondrial protein synthesis revealed no differences in apparent molecular weight and amount of radioactivity accumulated in apocytochrome b of the wild and recombinant strains.These results indicate that the accumulation in the same strain of the two mucidin-resistance mutations muc1muc2 results in an altered assembly of the noncovalently attached heme to the doubly mutated form of apocytochrome b.Publication n⁰ 1663 of the Biology Division of the Commission of European Communities. Financial help of the Fonds National de la Recherche Fondamentale Collective is also acknowledged