Coïc Eric, Feldman Taya, Landman Allison S, Haber James E
Department of Biology and Rosenstiel Center, Brandeis University, Waltham, MA 02454-9110, USA.
Genetics. 2008 May;179(1):199-211. doi: 10.1534/genetics.108.087189. Epub 2008 May 5.
In wild-type diploid cells, heteroallelic recombination between his4A and his4C alleles leads mostly to His+ gene conversions that have a parental configuration of flanking markers, but approximately 22% of recombinants have associated reciprocal crossovers. In rad52 strains, gene conversion is reduced 75-fold and the majority of His+ recombinants are crossover associated, with the largest class being half-crossovers in which the other participating chromatid is lost. We report that UV irradiating rad52 cells results in an increase in overall recombination frequency, comparable to increases induced in wild-type (WT) cells, and surprisingly results in a pattern of recombination products quite similar to RAD52 cells: gene conversion without exchange is favored, and the number of 2n - 1 events is markedly reduced. Both spontaneous and UV-induced RAD52-independent recombination depends strongly on Rad50, whereas rad50 has no effect in cells restored to RAD52. The high level of noncrossover gene conversion outcomes in UV-induced rad52 cells depends on Rad51, but not on Rad59. Those outcomes also rely on the UV-inducible kinase Dun1 and Dun1's target, the repressor Crt1, whereas gene conversion events arising spontaneously depend on Rad59 and Crt1. Thus, there are at least two Rad52-independent recombination pathways in budding yeast.
在野生型二倍体细胞中，his4A和his4C等位基因之间的异源等位基因重组大多导致His⁺基因转换，其侧翼标记具有亲本构型，但约22%的重组体伴有相互交叉。在rad52菌株中，基因转换减少了75倍，大多数His⁺重组体与交叉相关，最大的一类是半交叉，其中另一条参与的染色单体丢失。我们报道，紫外线照射rad52细胞会导致总体重组频率增加，与野生型（WT）细胞中诱导的增加相当，并且令人惊讶的是，其重组产物模式与RAD52细胞非常相似：倾向于不发生交换的基因转换，并且2n - 1事件的数量显著减少。自发的和紫外线诱导的不依赖Rad52的重组都强烈依赖于Rad50，而rad50对恢复到RAD52的细胞没有影响。紫外线诱导的rad52细胞中高水平的非交叉基因转换结果依赖于Rad51，但不依赖于Rad59。这些结果还依赖于紫外线诱导的激酶Dun1及其靶点阻遏物Crt1，而自发产生的基因转换事件依赖于Rad59和Crt1。因此，在芽殖酵母中至少存在两条不依赖Rad52的重组途径。
