Structure of DNA molecules in yeast meiosis

THE nuclear DNA of the yeast Saccharomyces cerevisiae has been the subject of a detailed electron microscopic examination^1,2. These studies have revealed long, continuous molecules of lengths up to 355 μm, which correspond to the molecular weights of nuclear DNA estimated from sedimentation analysis in sucrose gradients. Several replication structures (bubbles) were observed along single molecules^2,3, as found in other eukaryotes ^4,5. The most useful observations were made on selected replicating DNA³ and on DNA of mutants that were arrested just after the initiation of DNA synthesis⁶. We have started to study the structure of DNA molecules during meiosis because of its direct relevance to the process of recombination. Models to explain recombination (for review see ref. 7) are based mostly on genetic data from meiotic analysis, among which yeast tetrads occupy an important position. The various models have molecular implications which could best be tested by the direct examination and quantification of the interactions among DNA molecules, and between DNA and proteins, during meiosis.