The mitochondrial genome of wild-type yeast cells: V. Genome Evolution

Abstract

When degraded with the restriction enzymes HaeIII or HpaII, the mitochondrial DNAs from one Saccharomyces carlsbergensis and three genetically unrelated S. cerevisiae wild-type strains yielded 71 to 113 fragments ranging in molecular weight from 104 to 4×106. Genome unit sizes, calculated by adding up the molecular weights of all fragments produced by HaeIII, HpaII and, in some cases, HindII+III and EcoRI, were in the 52 to 54×106 range for the three S. cerevisiae strains, whereas a value lower by about 10% was found for the S. carlsbergensis strain. These values are in agreement with the physical size of circular twisted yeast mitochondrial DNA, as determined by electron microscopy (Hollenberg et al., 1970). Large differences in the electrophoretic patterns of HaeIII and HpaII fragments were found among the DNAs from different S. cerevisiae strains; S. cerevisiae and S. carlsbergensis DNAs showed only very few bands having the same mobility. Such differences appear to originate essentially from additions and deletions in the A+T-rich spacers and to be accompanied by a large preservation of gene order. Unequal crossing-over events at the spacers seem to be the source of additions and deletions and to underlie the evolution of the mitochondrial genome of yeast.