Osman F, Fortunato E A, Subramani S
Department of Biology, University of California at San Diego, La Jolla 92093-0322, USA.
Genetics. 1996 Feb;142(2):341-57. doi: 10.1093/genetics/142.2.341.
The Saccharomyces cerevisiae HO gene and MATa cutting site were used to introduce site-specific double-strand breaks (DSBs) within intrachromosomal recombination substrates in Schizosaccharomyces pombe. The recombination substrates consisted of nontandem direct repeats of ade6 heteroalleles. DSB induction stimulated the frequency of recombinants 2000-fold. The spectrum of DSB-induced recombinants depended on whether the DSB was introduced within one of the ade6 repeats or in intervening unique DNA. When the DSB was introduced within unique DNA, over 99.8% of the recombinants lacked the intervening DNA but retained one copy of ade6 that was wild type or either one of the heteroalleles. When the DSB was located in duplicated DNA, 77% of the recombinants were similar to the deletion types described above, but the single ade6 copy was either wild type or exclusively that of the uncut repeat. The remaining 23% of the induced recombinants were gene convertants with two copies of ade6 and the intervening sequences; the ade6 heteroallele in which the DSB was induced was the recipient of genetic information. Half-sectored colonies were isolated, analyzed and interpreted as evidence of heteroduplex DNA formation. The results are discussed in terms of current models for recombination.
酿酒酵母HO基因和MATa切割位点被用于在粟酒裂殖酵母的染色体内重组底物中引入位点特异性双链断裂（DSB）。重组底物由ade6杂合等位基因的非串联直接重复序列组成。DSB的诱导使重组频率提高了2000倍。DSB诱导的重组体谱取决于DSB是在ade6重复序列之一内引入还是在中间的独特DNA中引入。当DSB在独特DNA内引入时，超过99.8%的重组体缺少中间DNA，但保留了一个野生型或其中一个杂合等位基因的ade6拷贝。当DSB位于重复DNA中时，77%的重组体类似于上述缺失类型，但单个ade6拷贝是野生型或仅来自未切割重复序列的拷贝。其余诱导的重组体中有23%是具有两个ade6拷贝和中间序列的基因转换体；诱导DSB的ade6杂合等位基因是遗传信息的接受者。分离出半扇形菌落，进行分析并解释为异源双链DNA形成的证据。根据当前的重组模型对结果进行了讨论。
