Department of Biology, University of Iowa, Iowa City, IA 52245, USA; Interdisciplinary Graduate Program in Genetics, University of Iowa, Iowa City, IA 52245, USA.
Department of Biology, University of Iowa, Iowa City, IA 52245, USA; Interdisciplinary Graduate Program in Genetics, University of Iowa, Iowa City, IA 52245, USA.
Mol Cell. 2021 Apr 15;81(8):1816-1829.e5. doi: 10.1016/j.molcel.2021.02.004. Epub 2021 Feb 26.
Alternative lengthening of telomeres (ALT) is a recombination process that maintains telomeres in the absence of telomerase and helps cancer cells to survive. Yeast has been used as a robust model of ALT; however, the inability to determine the frequency and structure of ALT survivors hinders understanding of the ALT mechanism. Here, using population and molecular genetics approaches, we overcome these problems and demonstrate that contrary to the current view, both RAD51-dependent and RAD51-independent mechanisms are required for a unified ALT survivor pathway. This conclusion is based on the calculation of ALT frequencies, as well as on ultra-long sequencing of ALT products that revealed hybrid sequences containing features attributed to both recombination pathways. Sequencing of ALT intermediates demonstrates that recombination begins with Rad51-mediated strand invasion to form DNA substrates that are matured by a Rad51-independent ssDNA annealing pathway. A similar unified ALT pathway may operate in other organisms, including humans.
端粒的非经典延长（ALT）是一种重组过程，它在缺乏端粒酶的情况下维持端粒，并帮助癌细胞存活。酵母一直被用作 ALT 的强大模型；然而，无法确定 ALT 幸存者的频率和结构阻碍了对 ALT 机制的理解。在这里，我们使用群体和分子遗传学方法克服了这些问题，并证明与当前的观点相反，RAD51 依赖性和 RAD51 非依赖性机制对于统一的 ALT 幸存者途径都是必需的。这一结论是基于 ALT 频率的计算，以及对 ALT 产物的超长测序得出的，这些测序揭示了含有两种重组途径特征的杂交序列。对 ALT 中间体的测序表明，重组首先由 Rad51 介导的链入侵形成 DNA 底物，然后由 Rad51 非依赖性单链 DNA 退火途径使其成熟。类似的统一 ALT 途径可能在其他生物体中运作，包括人类。
