Genetic Recombination Catalyzed by Cell-free Extracts of Saccharomyces cerevisiae

Studies with Saccharomyces cerevisiae, which has been used as a model system for studying the mechanism(s) of genetic recombination, have documented a number of different types of recombination events. In haploid mitotic cells, both intrachromosomal recombination and sister chromatid exchange are known to occur (Szostak and Wu 1980; Jackson and Fink 1981; Klein and Petes 1981), and in diploid mitotic cells, recombination events can also occur between homologous chromosomes (Fogel and Mortimer 1971). Recombination during meiosis occurs at substantially higher frequencies than spontaneous mitotic recombination events (Fogel and Mortimer 1971). Furthermore, the frequency of gene conversion observed at different loci during meiosis is known to vary over a 30-fold range, suggesting that simple sequence homology is not the only requirement at the DNA level for recombination (Fogel et al. 1979). During meiosis, recombination appears to occur at the four-strand stage by a mechanism that yields both gene conversion events and...