Gene targeting at and distant from DNA breaks in yeast and human cells
Stuckey, Samantha Anne
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Here we developed multiple genetic systems through which genetic modifications driven by DNA breaks caused by the I-SceI nuclease can be assayed in the yeast Saccharomyces cerevisiae and in human cells. Using the delitto perfetto approach for site-directed mutagenesis in yeast, we generated isogenic strains in which we could directly compare the recombination potential of different I-SceI variants. By genetic engineering procedures, we generated constructs in human cells for testing the recombination activity of the same I-SceI variants. Both in yeast and human cells we performed gene correction experiments using oligonucleotides (oligos) following modification and/or optimization of existing gene targeting protocols and development of new ones. We demonstrated that an I-SceI nicking enzyme can stimulate recombination on the chromosome in S. cerevisiae at multiple genomic loci. We also demonstrated in yeast that an I-SceI-driven nick can activate recombination 10 kb distant from the initial site of the chromosomal lesion. Moreover we demonstrated that an I-SceI nick can stimulate recombination at the site of the nick at episomal and chromosomal loci in human cells. We showed that an I-SceI double-strand break (DSB) could trigger recombination up to 2 kb distant from the break at an episomal target locus in human cells, though the same was not observed for the nick. Overall, we demonstrated the capacity for I-SceI nick-induced recombination in yeast and human cells. Importantly, our findings reveal that the nick stimulates gene correction by oligos differently from a DSB lesion, as determined by genetic and molecular analyses in yeast and human cells. This research illustrates the promise of targeted gene correction following generation of a nick.