Lin Chi-Ying, Chang Hsih-Hsuan, Wu Kou-Juey, Tseng Shun-Fu, Lin Chuan-Chuan, Lin Chao-Po, Teng Shu-Chun
Department of Microbiology, National Taiwan University College of Medicine,Taipei 10018, Taiwan.
Eukaryot Cell. 2005 Feb;4(2):327-36. doi: 10.1128/EC.4.2.327-336.2005.
Telomere maintenance is required for chromosome stability, and telomeres are typically replicated by the telomerase reverse transcriptase. In both tumor and yeast cells that lack telomerase, telomeres are maintained by an alternative recombination mechanism. By using an in vivo inducible Cre-loxP system to generate and trace the fate of marked telomeric DNA-containing rings, the efficiency of telomere-telomere recombination can be determined quantitatively. We show that the telomeric loci are the primary sites at which a marked telomeric ring-containing DNA is observed among wild-type and surviving cells lacking telomerase. Marked telomeric DNAs can be transferred to telomeres and form tandem arrays through Rad52-, Rad50-, and polymerase delta-mediated recombination. Moreover, increases of extrachromosomal telomeric and Y' rings were observed in telomerase-deficient cells. These results imply that telomeres can use looped-out telomeric rings to promote telomere-telomere recombination in telomerase-deficient Saccharomyces cerevisiae.
端粒维持对于染色体稳定性是必需的，并且端粒通常由端粒酶逆转录酶进行复制。在缺乏端粒酶的肿瘤细胞和酵母细胞中，端粒通过一种替代重组机制得以维持。通过使用体内可诱导的Cre-loxP系统来产生并追踪含标记端粒DNA环的命运，可以定量测定端粒-端粒重组的效率。我们发现，在野生型细胞和缺乏端粒酶的存活细胞中，端粒位点是观察到含标记端粒环DNA的主要位点。标记的端粒DNA可以转移到端粒，并通过Rad52、Rad50和聚合酶δ介导的重组形成串联阵列。此外，在端粒酶缺陷细胞中观察到了染色体外端粒环和Y'环的增加。这些结果表明，在端粒酶缺陷的酿酒酵母中，端粒可以利用环出的端粒环来促进端粒-端粒重组。
