Biogenesis of mitochondria. 30

Summary Mitchondrial gene recombination in S. cerevisiae was investigated using four combinations of mitochondrial markers: [oli1-r ery1-r], [oli1-r spi2-r], [oli1-r spi3-r] and [oli1-r spi4-r] in cis bifactorial crosses to [oli-s ery-s spi-s] strains. A number of sensitive strains including representatives of both mating types and of diverse origin were used. The crosses were analysed for frequency and polarity of mitochondrial gene recombination as well as the frequency of transmission into the diploid progeny of individual mitochondrial determinants.The results show that the polarity of recombination varied markedly in crosses between a single pair of mitochondrial markers and many unrelated sensitive strains. For example, one series of crosses included polarity values of 1.7,0.34,0.081, and 0.021. Furthermore, there was also considerable variability in frequency of recombination and frequency of transmission of individual markers and these frequencies were not correlated in many cases with polarity values. However, in certain other crosses involving different marker combinations there was a correlation between extreme polarity, high recombination frequency and high transmission frequency of one marker. The results are not compatible with polarity being determined by a simple mitochondrial sex factor and suggest that several different interactions are operating which might include nuclear phenomena.