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Apr 22

Evolutionary conservation of a mitochondrial recombination junction

Dr. Stephan Zweifel, Professor of Biology, Carleton College

Monday, April 22nd, 2013
3:30 – 4:30 pm / Olin 141
Stephan Zweifel

   The pairing and exchange of DNA strands between homologous sequences leads to the formation of a four-way DNA junction.  These recombination intermediates, also known as Holliday junctions, are common to all molecular models of homologous recombination, and the resolution of these junctions is essential for subsequent chromosome separation.  Specialized endonucleases, termed resolvases, are responsible for cutting the four-way junction at the point of strand exchange.  One of the best-studied eukaryotic resolvases is the mitochondrial DNA cruciform-cutting enzyme (CCE1) isolated from the yeast Saccharomyces cerevisiae.  The absence of the mtDNA resolvase results in an aggregation of linked mtDNA molecules, and an elevated loss of the mitochondrial genome during mitotic division.  Recently, a homologous enzyme has been isolated from a distantly related species of yeast, Schizosaccharomyces pombe.  In both yeast species, the gene product is encoded by a nuclear gene and then imported into their respective mitochondria. To explore the functional homology of the two variants, we introduced the S. pombe gene into S. cerevisiae.  The S. pombe enzyme retains its mitochondrial targeting ability when expressed in S. cerevisiae, and the S. pombe enzyme can rescue the mitotic stability of an S. cerevisiae strain that lacks the CCE1 gene.  These results indicate that the mtDNA recombination junction-resolving enzymes from two evolutionary distant species of yeast are functionally conserved, raising the possibility that similar resolvases exist in other eukaryotic species.

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