Nucleic Acid Homologies Among Species of Saccharomyces

Abstract

Evolutionary divergence among species of the yeast genus Saccharomyces was estimated from measurements of deoxyribonucleic acid (DNA)/DNA and ribosomal ribonucleic acid (RNA)/DNA homology. Much diversity was found in the DNA base sequences with several species showing little or no homology to the three reference species, S. cerevisiae, S. lactis , and S. fragilis . These three reference species also showed little or no homology to each other. On the other hand the diversity among ribosomal RNA base sequences was small since most species showed a high degree of homology to the reference species. The arrangement of species based on ribosomal RNA homologies agrees in most cases with current taxonomic groupings. A yeast hybrid ( S. fragilis × S. lactis ) was shown to contain two nonhomologous genomes. A minimum genome size of 9.2 × 10 9 daltons for S. cerevisiae was calculated from the rate of DNA renaturation.