A model to explain the propagation of small dysfunctional mitochondrial DNAs in budding yeast

Mitochondrial DNA (mtDNA) in budding yeast is unstable, resulting in a high rate of spontaneous respiratory-deficient mutants [1]. These respiratory-deficient mutants (called petites) can, however, grow on fermentable media. A petite cell often contains small, incomplete mtDNA fragments, that replicate and pass on from generation to generation with no known function in the cell. These selfish mtDNAs often do better than wild type mtDNA and outcompete (suppress) them if they are present together in a cell [2]. The features that allow these selfish mtDNAs to outcompete wild type mtDNA, as well as the potential for mechanisms that select against selfish mtDNAs remains to be fully characterized. To address these questions we have characterized a set of spontaneous petite mitochondrial genomes, and developed a model to explain what features of their structure inform their suppressivity when mixed with wild type mtDNA.

[1] Dimitrov, et al. (2009). Polymorphisms in multiple genes contribute to the spontaneous mitochondrial genome instability of Saccharomyces cerevisiae S288C strains. Genetics, 183(1), 365–383.
[2] Zamaroczy, et al. (1981). The origins of replication of the yeast mitochondrial genome and the phenomenon of suppressivity. Nature, 292(July), 0–3.