Characterization of the cytochrome c gene from the starch-fermenting yeastSchwanniomyces occidentalis and its expression in bakers's yeast

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Abstract
A cytochrome c protein gene, CYC10, of the dextran‐ and starch‐fermenting yeast, Schwanniomyces occidentalis was cloned and characterized. The DNA sequence was determined, and the predicted amino acid sequence of the protein‐coding region shares close homologies to the cytochrome c genes. A. S. occidentalis strain with a disruption of the gene revealed that CYC10 was the only functional cytochrome c protein‐encoding gene in S. occidentalis, unlike the two cytochrome c protein genes (CYC1 and CYC7) in Saccharomyces cerevisiaear The CYC10 gene was oxygen‐induced but not subject to catabolite repression. The expression of the CYC10 gene was studied in the heterologous yeast. S. cerevisiae. The oxygen induction of the gene was found to be identical to that of the CYC1 gene, indecating these two genes share similar or closely related cis‐ and trans‐ acting oxygen regulatory elements. However, the CYC10 gene was glucose repressed in S. cerevisiae strains; a phenomenon which was not observed in the native S. accidentalis cells. Search in the 5′ unstranslated region of the CYC10 gene revealed some homologies at −425 to −405 to UAS1 of the S. cerevisiae CYC1 gene. A deletion of a segment of upstream region including this sequence abolished expression in S. cerevisiae. Finally the phylogenetic relationships of different yeasts and fungi were determined based upon the amino acid sequences of the cytochrome c proteins. These relationships do not completely agree with classical divisions.