Structural aspects of RecA-dependent homologous strand exchange involving human telomeric DNA.
Structural aspects of RecA-dependent homologous strand exchange involving human telomeric DNA.
复制标题
涉及人类端粒 DNA 的 RecA 依赖性同源链交换的结构方面。
DOI：
10.1021/bi047735r
复制
发表时间：
2005
期刊：
影响因子：
--
通讯作者：
Levene,StephenD
中科院分区：
文献类型：
--
作者：
Zein,SimaS;Levene,StephenD
人类细胞和其他脊椎动物的端粒 DNA 序列由长 d(TTAGGG) 重复序列组成。在体细胞中，端粒缩短每次细胞分裂，缩短作为有丝分裂时钟，计算细胞分裂并最终导致细胞衰老。端粒长度主要由核糖核蛋白端粒酶维持。然而，不可忽视的一部分人类细胞使用基于重组的端粒维持机制，称为端粒替代维持（ALT）。尽管 ALT 的分子机制尚不清楚，但原核生物和真核生物中富含 GT 的序列相对于非富含 GT 的 DNA 表现出高水平的重组。我们发现大肠杆菌RecA 蛋白介导的人类端粒链交换复合物与非端粒序列形成的端粒链交换复合物不同。此外，端粒链交换中间体与涉及非端粒序列的中间体不同，表现出形成更高阶核蛋白结构的倾向。我们认为 RecA 链交换复合物组装中固有的强 DNA 解旋活性促进了人类端粒位点替代 DNA 结构的形成。将这些非规范结构组织成涉及多个 DNA 双链体的高阶复合物可以促进不同 DNA 分子上同源性的搜索，并为理解端粒维持的重组依赖性机制提供框架。
Telomeric DNA sequences in human cells and those of other vertebrates consist of long d(TTAGGG) repeats. In somatic cells, telomeres shorten every cell division with shortening serving as a mitotic clock that counts cell divisions and ultimately results in cellular senescence. Telomere length is principally maintained by a ribonucleoprotein, telomerase. However, a non-negligible proportion of human cells use a recombination-based mechanism for telomere maintenance, termed alternative maintenance of telomeres (ALT). Although the molecular mechanism of ALT is not known, GT-rich sequences in prokaryotes and eukaryotes display high levels of recombination relative to those of non-GT-rich DNA. We show that human telomeric strand-exchange complexes mediated byEscherichia coliRecA protein differ from those formed with nontelomeric sequences. Moreover, telomeric strand-exchange intermediates, unlike those involving nontelomeric sequences, exhibit a tendency to form higher-order nucleoprotein structures. We propose that the strong DNA unwinding activity inherent in the assembly of the RecA strand-exchange complex promotes the formation of alternative DNA structures at human telomeric loci. Organization of these noncanonical structures into higher-order complexes involving multiple DNA duplexes could facilitate the search for homology on different DNA molecules and provide a framework for understanding recombination-dependent mechanisms of telomere maintenance.