Yu Jianhua, Marshall Kelly, Yamaguchi Miyuki, Haber James E, Weil Clifford F
Department of Agronomy, Purdue University, West Lafayette, Indiana 47907-1150, USA.
Mol Cell Biol. 2004 Feb;24(3):1351-64. doi: 10.1128/MCB.24.3.1351-1364.2004.
The maize, cut-and-paste transposon Ac/Ds is mobile in Saccharomyces cerevisiae, and DNA sequences of repair products provide strong genetic evidence that hairpin intermediates form in host DNA during this transposition, similar to those formed for V(D)J coding joints in vertebrates. Both DNA strands must be broken for Ac/Ds to excise, suggesting that double-strand break (DSB) repair pathways should be involved in repair of excision sites. In the absence of homologous template, as expected, Ac excisions are repaired by nonhomologous end joining (NHEJ) that can involve microhomologies close to the broken ends. However, unlike repair of endonuclease-induced DSBs, repair of Ac excisions in the presence of homologous template occurs by gene conversion only about half the time, the remainder being NHEJ events. Analysis of transposition in mutant yeast suggests roles for the Mre11/Rad50 complex, SAE2, NEJ1, and the Ku complex in repair of excision sites. Separation-of-function alleles of MRE11 suggest that its endonuclease function is more important in this repair than either its exonuclease or Rad50-binding properties. In addition, the interstrand cross-link repair gene PSO2 plays a role in end joining hairpin ends that is not seen in repair of linearized plasmids and may be involved in positioning transposase cleavage at the transposon ends.
玉米的剪切粘贴转座子Ac/Ds在酿酒酵母中具有移动性，修复产物的DNA序列提供了有力的遗传学证据，表明在这种转座过程中，宿主DNA中会形成发夹中间体，这与脊椎动物V(D)J编码接头形成的中间体类似。Ac/Ds切除需要两条DNA链都断裂，这表明双链断裂（DSB）修复途径应该参与切除位点的修复。正如预期的那样，在没有同源模板的情况下，Ac切除通过非同源末端连接（NHEJ）进行修复，该过程可能涉及靠近断裂末端的微同源性。然而，与内切酶诱导的DSB修复不同，在有同源模板存在的情况下，Ac切除的修复只有大约一半的时间通过基因转换发生，其余为NHEJ事件。对突变酵母中转座的分析表明，Mre11/Rad50复合物、SAE2、NEJ1和Ku复合物在切除位点的修复中发挥作用。MRE11的功能分离等位基因表明，其内切酶功能在这种修复中比其核酸外切酶或Rad50结合特性更重要。此外，链间交联修复基因PSO2在发夹末端的末端连接中发挥作用，这在线性化质粒的修复中未见，可能参与转座酶在转座子末端的切割定位。
