Department of Molecular Biology, Graduate School of Science, Gakushuin University, Tokyo 1718588, Japan.
Genetics. 2022 Aug 30;222(1). doi: 10.1093/genetics/iyac115.
Ultraviolet-induced DNA lesions impede DNA replication and transcription and are therefore a potential source of genome instability. Here, we performed serial transfer experiments on nucleotide excision repair-deficient (rad14Δ) yeast cells in the presence of chronic low-dose ultraviolet irradiation, focusing on the mechanisms underlying adaptive responses to chronic low-dose ultraviolet irradiation. Our results show that the entire haploid rad14Δ population rapidly becomes diploid during chronic low-dose ultraviolet exposure, and the evolved diploid rad14Δ cells were more chronic low-dose ultraviolet-resistant than haploid cells. Strikingly, single-stranded DNA, but not pyrimidine dimer, accumulation is associated with diploid-dependent fitness in response to chronic low-dose ultraviolet stress, suggesting that efficient repair of single-stranded DNA tracts is beneficial for chronic low-dose ultraviolet tolerance. Consistent with this hypothesis, homologous recombination is essential for the rapid evolutionary adaptation of diploidy, and rad14Δ cells lacking Rad51 recombinase, a key player in homologous recombination, exhibited abnormal cell morphology characterized by multiple RPA-yellow fluorescent protein foci after chronic low-dose ultraviolet exposure. Furthermore, interhomolog recombination is increased in chronic low-dose ultraviolet-exposed rad14Δ diploids, which causes frequent loss of heterozygosity. Thus, our results highlight the importance of homologous recombination in the survival and genomic stability of cells with unrepaired lesions.
紫外线诱导的 DNA 损伤会阻碍 DNA 复制和转录，因此是基因组不稳定的潜在来源。在这里，我们在慢性低剂量紫外线照射下对核苷酸切除修复缺陷型（rad14Δ）酵母细胞进行了连续传代实验，重点研究了对慢性低剂量紫外线照射适应反应的机制。我们的结果表明，在慢性低剂量紫外线暴露下，整个单倍体 rad14Δ 群体迅速变为二倍体，并且进化而来的二倍体 rad14Δ 细胞比单倍体细胞对慢性低剂量紫外线更具抗性。引人注目的是，单链 DNA 的积累，而不是嘧啶二聚体的积累，与二倍体依赖性对慢性低剂量紫外线应激的适应性相关，表明有效修复单链 DNA 片段有利于慢性低剂量紫外线耐受。与这一假设一致，同源重组对于二倍体的快速进化适应是必不可少的，并且缺乏同源重组关键因子 Rad51 重组酶的 rad14Δ 细胞在慢性低剂量紫外线暴露后表现出异常的细胞形态，其特征是出现多个 RPA-黄色荧光蛋白焦点。此外，慢性低剂量紫外线暴露下的 rad14Δ 二倍体中同源重组增加，导致频繁的杂合性丢失。因此，我们的结果强调了同源重组在未修复损伤的细胞的存活和基因组稳定性中的重要性。
