Malkova A, Ross L, Dawson D, Hoekstra M F, Haber J E
Rosenstiel Center, Brandeis University, Waltham, Massachusetts 02254-9110, USA.
Genetics. 1996 Jun;143(2):741-54. doi: 10.1093/genetics/143.2.741.
Meiotic recombination in Saccharomyces cerevisiae is initiated by double- strand breaks (DSBs). We have developed a system to compare the properties of meiotic DSBs with those created by the site-specific HO endonuclease. HO endonuclease was expressed under the control of the meiotic-specific SPO13 promoter, creating a DSB at a single site on one of yeast's 16 chromosomes. In Rad+ strains the times of appearance of the HO-induced DSBs and of subsequent recombinants are coincident with those induced by normal meiotic DSBs. Physical monitoring of DNA showed that SPO13: : HO induced gene conversions both in Rad+ and in rad50 delta cells that cannot initiate normal meiotic DSBs. We find that the RAD50 gene is important, but not essential, for recombination even after a DSB has been created in a meiotic cell. In rad50 delta cells, some DSBs are not repaired until a broken chromosome has been packaged into a spore and is subsequently germinated. This suggests that a broken chromosome does not signal an arrest of progression through meiosis. The recombination defect in rad50 delta diploids is not, however, meiotic specific, as mitotic rad50 diploids, experiencing an HO-induced DSB, exhibit similar departures from wild-type recombination.
酿酒酵母中的减数分裂重组由双链断裂（DSB）引发。我们开发了一个系统，用于比较减数分裂DSB与位点特异性HO核酸内切酶产生的DSB的特性。HO核酸内切酶在减数分裂特异性SPO13启动子的控制下表达，在酵母16条染色体之一的单个位点上产生一个DSB。在Rad⁺菌株中，HO诱导的DSB和随后重组体出现的时间与正常减数分裂DSB诱导的时间一致。对DNA的物理监测表明，SPO13::HO在Rad⁺和不能启动正常减数分裂DSB的rad50Δ细胞中均诱导基因转换。我们发现，RAD50基因对于重组很重要，但不是必需的，即使在减数分裂细胞中产生DSB之后也是如此。在rad50Δ细胞中，一些DSB直到断裂的染色体被包装到孢子中并随后萌发才被修复。这表明断裂的染色体不会发出减数分裂进程停滞的信号。然而，rad50Δ二倍体中的重组缺陷并非减数分裂特异性缺陷，因为经历HO诱导DSB的有丝分裂rad50二倍体与野生型重组表现出类似的偏差。
