Sequence of the mitochondrial gene encoding subunit I of cytochrome oxidase in Saccharomyces douglasii

We have determined the complete sequence of the mitochondrial (mt) gene (COXI) coding for cytochrome oxidase subunit I of Saccharomyces douglasii. This gene is 7238 bp long and includes four introns. The salient feature of the S. douglasii COXI gene is the presence of two introns, Sd.ai1 and Sd.ai2, which have not been observed in S. cerevisiae genes. Both are group-I introns and are located at novel positions compared with the S. cerevisiae COXI. Interestingly, one of these introns (the second one) is inserted at the same position as intron 2 of COXI of Kluyveromyces lactis and also as intron 8 of the same gene in Podospora anserina. The ORFs contained in these three introns display a high degree of similarity. Comparisons of exonic and intronic sequences of the COXI of two Saccharomyces species reinforces our previous conclusions: the evolution of mt genes in yeast obeys different rules to those found in vertebrates.