Yeast Genetics and Molecular Biology 2000
University of Washington
Seattle, Washington USA
July 2000

Name: Allers, Thorsten
Mailing Address: Lab of Biochem, Bg 37 Rm 4C03, National Cancer Institute, NIH, 37 Convent Drive, Bethesda, MD 20892, USA
Email Address: allers@sunspot.nci.nih.gov
Phone & FAX numbers: +1 301 496 3393 & +1 301 402 7437

#057

Physical and genetical analysis of heteroduplex DNA and intermediate structures formed during meiotic recombination in Saccharomyces cerevisiae.
Thorsten Allers, Michael Lichten
Lab of Biochem, Bg 37 Rm 4C03, National Cancer Institute, NIH, 37 Convent Drive, Bethesda, MD 20892, USA

During meiosis, homologous chromosomes must pair their DNA in order to exchange genetic information. Heteroduplex DNA (hDNA) has been an essential feature of every model for genetic recombination - it is predicted to play an early role, and to be associated with Holliday junction intermediates. However, hDNA has been detected only late during meiosis in yeast, and studies of Holliday junction intermediates have failed to detect the presence of associated hDNA. These observations challenge the double-strand break repair model for meiotic recombination. We have developed a method of DNA extraction that preserves branched recombination intermediates, and a physical assay for hDNA based on palindromic DNA markers, which escape mismatch correction in S. cerevisiae. We have found that a significant proportion of Holliday junction intermediates contain DNA strands consistent with associated hDNA. Additionally, we are able to detect hDNA that is non-crossover for flanking markers 1/2 h in advance of crossover-associated hDNA. This delay is exaggerated in ndt80 mutants, where Holliday junction intermediates are formed but not resolved, and accumulate to high levels. Very few crossovers or crossover-associated hDNA are found in ndt80 meiosis, and yet non-crossover hDNA appears with normal kinetics and at normal levels. These results indicate that non-crossover and crossover-associated hDNA are not formed by alternative resolutions of the same Holliday junction intermediate.

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