Dipartimento di Biologia e Biotecnologie 'Charles Darwin', Sapienza Università di Roma, 00185 Rome, Italy.
Nucleic Acids Res. 2013 Jul;41(13):6490-500. doi: 10.1093/nar/gkt365. Epub 2013 May 15.
Vertebrate-like T2AG3 telomeres in tlc1-h yeast consist of short double-stranded regions and long single-stranded overhang (G-tails) and, although based on Tbf1-capping activity, they are capping deficient. Consistent with this idea, we observe Y' amplification because of homologous recombination, even in the presence of an active telomerase. In these cells, Y' amplification occurs by different pathways: in Tel1(+) tlc1h cells, it is Rad51-dependent, whereas in the absence of Tel1, it depends on Rad50. Generation of telomeric G-tail, which is cell cycle regulated, depends on the MRX (Mre11-Rad50-Xrs2) complex in tlc1h cells or is MRX-independent in tlc1h tel1Δ mutants. Unexpectedly, we observe telomere elongation in tlc1h lacking Rad51 that seems to act as a telomerase competitor for binding to telomeric G-tails. Overall, our results show that Tel1 and Rad51 have multiple roles in the maintenance of vertebrate-like telomeres in yeast, supporting the idea that they may participate to evolutionary conserved telomere protection mechanism/s acting at uncapped telomeres.
在 tlc1-h 酵母中，脊椎动物样 T2AG3 端粒由短的双链区和长的单链突出端（G 尾巴）组成，尽管基于 Tbf1 加帽活性，但它们缺乏加帽能力。与这一观点一致，我们观察到 Y'扩增是由于同源重组，即使存在活性端粒酶也是如此。在这些细胞中，Y'扩增通过不同的途径发生：在 Tel1(+) tlc1h 细胞中，它依赖于 Rad51，而在没有 Tel1 的情况下，它依赖于 Rad50。端粒 G 尾巴的产生是细胞周期调控的，这取决于 tlc1h 细胞中的 MRX（Mre11-Rad50-Xrs2）复合物，或者在 tlc1h tel1Δ 突变体中是 MRX 独立的。出乎意料的是，我们观察到在缺乏 Rad51 的 tlc1h 中存在端粒延长，这似乎作为一种端粒酶竞争蛋白，与端粒 G 尾巴结合。总的来说，我们的结果表明，Tel1 和 Rad51 在酵母中维持脊椎动物样端粒中具有多种作用，支持它们可能参与到作用于无帽端粒的进化保守端粒保护机制/的观点。
