Department of Molecular and Cellular Biology, University of Arizona, Tucson, Arizona, United States of America.
Department of Microbiology and Infectiology, Université de Sherbrooke, Sherbrooke, Quebec, Canada.
PLoS Genet. 2020 Apr 14;16(4):e1008733. doi: 10.1371/journal.pgen.1008733. eCollection 2020 Apr.
In budding yeast, Cdc13, Stn1, and Ten1 form the telomere-binding heterotrimer CST complex. Here we investigate the role of Cdc13/CST in maintaining genome stability by using a Chr VII disome system that can generate recombinants, chromosome loss, and enigmatic unstable chromosomes. In cells expressing a temperature sensitive CDC13 allele, cdc13F684S, unstable chromosomes frequently arise from problems in or near a telomere. We found that, when Cdc13 is defective, passage through S phase causes Exo1-dependent ssDNA and unstable chromosomes that are then the source for additional chromosome instability events (e.g. recombinants, chromosome truncations, dicentrics, and/or chromosome loss). We observed that genome instability arises from a defect in Cdc13's function during DNA replication, not Cdc13's putative post-replication telomere capping function. The molecular nature of the initial unstable chromosomes formed by a Cdc13-defect involves ssDNA and does not involve homologous recombination nor non-homologous end joining; we speculate the original unstable chromosome may be a one-ended double strand break. This system defines a link between Cdc13's function during DNA replication and genome stability in the form of unstable chromosomes, that then progress to form other chromosome changes.
在芽殖酵母中，Cdc13、Stn1 和 Ten1 形成端粒结合异三聚体 CST 复合物。在这里，我们通过使用 ChrVII 二倍体系统来研究 Cdc13/CST 在维持基因组稳定性方面的作用，该系统可以产生重组体、染色体丢失和神秘不稳定的染色体。在表达温度敏感 CDC13 等位基因 cdc13F684S 的细胞中，不稳定的染色体经常由于端粒内或附近的问题而产生。我们发现，当 Cdc13 有缺陷时，通过 S 期会导致 Exo1 依赖性单链 DNA 和不稳定的染色体，然后这些染色体是额外染色体不稳定性事件（例如重组体、染色体缺失、双着丝粒和/或染色体丢失）的来源。我们观察到，基因组不稳定性是由于 Cdc13 在 DNA 复制过程中的功能缺陷引起的，而不是 Cdc13 假定的复制后端粒加帽功能。由 Cdc13 缺陷形成的初始不稳定染色体的分子性质涉及单链 DNA，不涉及同源重组，也不涉及非同源末端连接；我们推测原始不稳定染色体可能是一个单端双链断裂。该系统以不稳定染色体的形式定义了 Cdc13 在 DNA 复制过程中的功能与基因组稳定性之间的联系，然后这些染色体进一步发展形成其他染色体变化。
