Fouché Nicole, Ozgür Sezgin, Roy Debasmita, Griffith Jack D
Department of Biochemistry and Biophysics, Lineberger Comprehensive Cancer Center, The University of North Carolina, Chapel Hill, NC 27599, USA.
Nucleic Acids Res. 2006;34(20):6044-50. doi: 10.1093/nar/gkl757. Epub 2006 Oct 28.
Among several different types of repetitive sequences found in the human genome, this study has examined the telomeric repeat, necessary for the protection of chromosome termini, and the disease-associated triplet repeat (CTG).(CAG)n. Evidence suggests that replication of both types of repeats is problematic and that a contributing factor is the repetitive nature of the DNA itself. Here we have used electron microscopy to investigate DNA structures formed at replication forks on large model DNAs containing these repeat sequences, in an attempt to elucidate the contributory effect that these repetitive DNAs may have on their replication. Visualization of the DNA revealed that there is a high propensity for a paused replication fork to spontaneously regress when moving through repetitive DNAs, and that this results in a four-way chickenfoot intermediate that could present a significant block to replication in vivo, possibly leading to unwanted recombination events, amplifications or deletions.
在人类基因组中发现的几种不同类型的重复序列中，本研究检测了对染色体末端保护至关重要的端粒重复序列以及与疾病相关的三联体重复序列（CTG）（CAG）n。有证据表明，这两种类型的重复序列的复制都存在问题，而一个促成因素是DNA本身的重复性质。在这里，我们利用电子显微镜研究了在含有这些重复序列的大型模型DNA上复制叉处形成的DNA结构，试图阐明这些重复DNA对其复制可能产生的促成作用。对DNA的观察显示，当复制叉在重复DNA中移动时，有很高的倾向会自发地倒退，这会导致形成一种四向鸡足状中间体，这可能会在体内对复制造成重大阻碍，可能导致不必要的重组事件、扩增或缺失。
