High-Resolution Mapping of Spontaneous Mitotic Recombination Hotspots on the 1.1 Mb Arm of Yeast Chromosome IV

Although homologous recombination is an important pathway for the repair of double-stranded DNA breaks in mitotically dividing eukaryotic cells, these events can also have negative consequences, such as loss of heterozygosity (LOH) of deleterious mutations. We mapped about 140 spontaneous reciprocal crossovers on the right arm of the yeast chromosome IV using single-nucleotide-polymorphism (SNP) microarrays. Our mapping and subsequent experiments demonstrate that inverted repeats of Ty retrotransposable elements are mitotic recombination hotspots. We found that the mitotic recombination maps on the two homologs were substantially different and were unrelated to meiotic recombination maps. Additionally, about 70% of the DNA lesions that result in LOH are likely generated during G1 of the cell cycle and repaired during S or G2. We also show that different genetic elements are associated with reciprocal crossover conversion tracts depending on the cell cycle timing of the initiating DSB.尽管同源重组是进行有丝分裂的真核细胞修复DNA双链断裂的重要途径，但这类事件也可能带来负面后果，例如有害突变的杂合性丢失（loss of heterozygosity, LOH）。我们采用单核苷酸多态性（single-nucleotide-polymorphism, SNP）芯片，在酵母IV号染色体右臂上完成了约140个自发相互交换事件的定位分析。我们的定位分析与后续实验证实，Ty反转录转座子（Ty retrotransposable elements）的反向重复序列是有丝分裂重组热点。研究显示，两条同源染色体上的有丝分裂重组图谱差异显著，且与减数分裂重组图谱完全无关。此外，约70%引发杂合性丢失的DNA损伤可能产生于细胞周期的G1期，并在S期或G2期完成修复。我们还发现，根据起始双链断裂的细胞周期时序差异，与之对应的相互交换转换区段所关联的遗传元件也有所不同。