Determination of the nuclear DNA content of Saccharomyces cerevisiae and implications for the organization of DNA in yeast chromosomes.

The DNA content of the nucleus of the yeast Saccharomyces cerevisiae has been determined by both renaturation kinetics and DNA per cell measurements. Renaturation kinetics experiments were performed by following the decrease of optical hyperchromicity at 260 nm and by hydroxyapatite chromatography. DNA per cell measurements were made by the diaminobenzoic acid method and by the ethidium bromide method of Klotz &; Zimm (1972b). The conclusion from the above experiments is that the S. cerevisiae nucleus contains 9 × 10⁹ ± 2 × 10⁹ daltons of DNA. Previously we (Lauer &; Klotz, 1975) had measured the molecular weight of the largest piece of DNA in the yeast nucleus to be 2 × 10⁹ ± 0.2 × 10⁹. Here we extend this work by using a more highly protein-denaturing buffer system and conclude that the largest piece of DNA in the S. cerevisiae nucleus contains 1.5 × 10⁹ to 2.2 × 10⁹ daltons of DNA in both haploid and diploid cell lysates. From genetics, the largest yeast chromosome should contain 13% of the genome, or 0.9 × 10⁹ to 1.5 × 10⁹ daltons of DNA (using our DNA per cell range). Thus, the large DNA we measure contains from one to two times the amount of the DNA predicted from genetics to be in the largest chromosome. In light of these new data, viscoelastic measurements on yeast DNA are now consistent with the idea that each chromosome contains one piece of DNA.