The mitochondrial reading frame RF3 is a functional gene in Saccharomyces uvarum

The yeast mitochondrial genome contains three reading frames, RF1, RF2, and RF3, which are related to the group I maturases, though they are not intronic sequences. In the Saccharomyces cerevisiae strain D273-10B/A, these reading frames are interrupted by G + C-rich sequences (GC clusters) which break the frames. In the present work we described a Saccharomyces uvarum strain which possesses a RF3 continuous sequence devoid of GC clusters. Moreover, our results strongly suggest that in the same strain RF2 and RF1 are also continuous sequences. As all three RFs belong to transcription units which are highly expressed, it is most reasonable to assume that RF1, RF2, and RF3 are functional genes. Furthermore, we have discovered a rule which seems to explain the transposition of GC clusters, considered as mobile elements, in the mitochondrial genome.