The fundamental mechanisms of meiosis in eukaryotic organisms have proven accessible to genetic analysis in budding yeast, but crucial interactions of the functional components with chromosomal DNA remain obscure. Genetic experiments have revealed a key role for the product of the HOP1 gene in forming the lateral elements of the synaptonemal complex and in promoting early events in recombination. In vitro assays have demonstrated that Hopi binds with high avidity to DNA containing structures known as G-quartets or quadriplex DNA -- an unusual Hoogsteen-bonded configuration dependent on the presence of multiple poly-deoxyguanine arrays. This work has also proven that Hopi is capable of mediating G-quartet formation in vitro, and parallel studies have shown how insertions into the chromosome of sequences capable of folding into this state can enhance the level of meiotic recombination. A major focus of the current project is to establish the correspondence between Hop 1/G-quartet interactions and the role of Hopi in meiotic synapsis and recombination. Specific segments of the HOP1 gene will be mutated and tested for associated deficiencies in various meiotic functions that are assayable in vivo and can also be tested for their ability to interact with DNA in vitro. An expanded set of DNA insertions capable of G-quartet formation should help to establish how Hopi might mediate the associated recombinational stimulation, and these new insertions will support efforts to identify other relevant genes by use of robotic assays employing the comprehensive set of yeast deletions. This research should provide a better understanding of how Hop! performs its role in yeast meiosis, perhaps shedding light on universal meiotic mechanisms that may specifically fail in nondisjunctional pathways, such as that leading to Down?s syndrome. Findings may also provide a better understanding of Hoogsteen pairing, which has been implicated in such debilitating genetic disorders as Bloom?s, Werner?s, and fragile-X syndromes.