Size Diversity and Sequence Rearrangements in Mitochondrial DNAs from Yeasts

Abstract

The most striking feature of mtDNAs from yeasts is their large size diversity. Lengths in petite positive yeasts vary from 18.9 kilobase pairs (kbp) in Torulopsis glabrata to around 108 kbp in Brettanomyces custersii (Table 1). Mapping of restriction endonuclease sites has shown that yeast mtDNAs are circular, and in some instances this has been confirmed by electron microscopy (Table 1).

In seeking an explanation for yeast mtDNA length heterogeneity, we can reject the notion that size is a direct measure of genetic complexity, because detailed studies of Saccharomyces cerevisiae mtDNA have shown that at least 50% of the 78-kbp molecule is composed of A + T-rich sequences that cannot code for protein (Prunell and Bernardi 1974).

An alternative explanation is that yeast mtDNAs differ only in the amount of noncoding sequences that separate a constant number of genes. This idea now needs modification in view of the recent discoveries with S. cerevisiae mtDNA that the genes for cytochrome b and cytochrome oxidase subunit I (COI) are disrupted with intervening sequences (Haid et al. 1979;Bonitz et al. 1980;Lazowska et al. 1980;Nobrega and Tzagoloff 1980; Dhawale et al. 1981). Although the coding regions of these two genes are only 1155 bp and 1533 bp, respectively, the lengths of the sequences spanned are approximately 8.5 kbp and 10 kbp (Bonitz et al. 1980; Nobrega and Tzagoloff 1980), which adds up to nearly the length of the T. glabrata mtDNA (18.9 kbp). These observations raised the possibility that the T. glabrata mtDNA, and...