Hunter N, Kleckner N
Department of Molecular and Cellular Biology, Harvard University, 7 Divinity Avenue, Cambridge, MA 02138, USA.
Cell. 2001 Jul 13;106(1):59-70. doi: 10.1016/s0092-8674(01)00430-5.
We identify a novel meiotic recombination intermediate, the single-end invasion (SEI), which occurs during the transition from double-strand breaks (DSBs) to double-Holliday junction (dHJs). SEIs are products of strand exchange between one DSB end and its homolog. The structural asymmetry of SEIs indicates that the two ends of a DSB interact with the homolog in temporal succession, via structurally (and thus biochemically) distinct processes. SEIs arise surprisingly late in prophase, concomitant with synaptonemal complex (SC) formation. These and other data imply that SEIs are preceded by nascent DSB-partner intermediates, which then undergo selective differentiation into crossover and noncrossover types, with SC formation and strand exchange as downstream consequences. Late occurrence of strand exchange provides opportunity to reverse recombinational fate even after homologs are coaligned and/or synapsed. This feature can explain crossover suppression between homeologous and structurally heterozygous chromosomes.
我们鉴定出一种新型减数分裂重组中间体——单端侵入（SEI），它发生在从双链断裂（DSB）向双Holliday连接体（dHJ）转变的过程中。SEI是一个DSB末端与其同源物之间链交换的产物。SEI的结构不对称表明，DSB的两端通过结构上（进而生化上）不同的过程，在时间上相继与同源物相互作用。SEI出人意料地在前期晚期出现，与联会复合体（SC）的形成同时发生。这些以及其他数据表明，在SEI之前存在新生的DSB-配对中间体，这些中间体随后经历选择性分化，形成交叉型和非交叉型，而SC的形成和链交换是其下游结果。链交换的晚期发生，即使在同源物配对和/或联会之后，也为逆转重组命运提供了机会。这一特性可以解释同源染色体和结构杂合染色体之间的交叉抑制现象。
