Kaytor M D, Livingston D M
Department of Biochemistry, University of Minnesota, Minneapolis 55455.
Genetics. 1994 Aug;137(4):933-44. doi: 10.1093/genetics/137.4.933.
We have screened for mutations of the Saccharomyces cerevisiae RAD52 gene which confer a temperature-sensitive (ts) phenotype with respect to either the repair of DNA lesions caused by methyl methanesulfonate (MMS) or the recombination of an intrachromosomal recombination reporter. We were readily able to isolate alleles ts for the repair of lesions caused by MMS but were unable to find alleles with a severe ts deficiency in intrachromosomal recombination. We extensively characterized four strains conferring ts growth on MMS agar. These strains also exhibit ts survival when exposed to gamma-radiation or when the HO endonuclease is constitutively expressed. Although none of the four alleles confers a severe ts defect in intrachromosomal recombination, two confer significant defects in tests of mitotic, interchromosomal recombination carried out in diploid strains. The mutant diploids sporulate, but the two strains with defects in interchromosomal recombination have reduced spore viability. Meiotic recombination is not depressed in the two diploids with reduced spore viability. Thus, in the two strains with reduced spore viability, defects in mitotic and meiotic recombination do not correlate. Sequence analysis revealed that in three of the four ts alleles the causative mutations are in the first one-third of the open reading frame while the fourth is in the C-terminal third.
我们筛选了酿酒酵母RAD52基因的突变，这些突变在修复由甲磺酸甲酯（MMS）引起的DNA损伤或染色体内部重组报告基因的重组方面表现出温度敏感（ts）表型。我们很容易就能分离出对MMS引起的损伤修复具有ts表型的等位基因，但未能找到在染色体内部重组中存在严重ts缺陷的等位基因。我们对四株在MMS琼脂上生长呈ts表型的菌株进行了广泛的表征。当暴露于γ射线或HO内切核酸酶组成型表达时，这些菌株也表现出ts存活。虽然这四个等位基因中没有一个在染色体内部重组中导致严重的ts缺陷，但有两个在二倍体菌株中进行的有丝分裂、染色体间重组测试中导致了显著的缺陷。突变二倍体能够形成孢子，但染色体间重组有缺陷的两个菌株的孢子活力降低。在孢子活力降低的两个二倍体中，减数分裂重组并未受到抑制。因此，在孢子活力降低的两个菌株中，有丝分裂和减数分裂重组的缺陷并不相关。序列分析表明，在四个ts等位基因中的三个中，致病突变位于开放阅读框的前三分之一，而第四个位于C端的三分之一。
