Consequences of unique double-stranded breaks in yeast chromosomes: death or homozygosis.
Fairhead C. | Dujon B.
A system has been developed in which a unique double-stranded break (DSB) can be introduced into a yeast chromosome during mitotic growth. The recognition site for the endonuclease 1-Sce1 was inserted at different places in the yeast genome in haploid and diploid cells expressing this endonuclease. Induction of the break in haploids results in cell death if no intact copy of the cleaved region is present in the cell. If such a copy is provided on a plasmid, as an ectopic gene duplication, or on a homologous chromosome, the break can be repaired. Repair results in two identical copies in the genome of the locus which has been cut. This phenomenon was called homozygotization by reference to diploids heterozygous for the cut size in which repair leads to homozygosis at this site. The efficiencies of repair were compared in the various topological situations examined, and conclude that some mechanism must search for regions of homology to both sides of the DSB and that repair is successful only if the homologies are provided by the same template molecule.
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