Intramolecular quadruplex conformation of human telomeric DNA assessed with 125I-radioprobing
Intramolecular quadruplex conformation of human telomeric DNA assessed with 125I-radioprobing
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DOI：
10.1093/nar/gkh875
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发表时间：
2004-01-01
影响因子：
14.9
通讯作者：
Panyutin, IG
中科院分区：
文献类型：
--
作者：
He, YJ;Neumann, RD;Panyutin, IG
重复的非编码DNA序列d(TTAGGG)(N)存在于所有人类染色体的端粒末端。这些重复序列可以采用多种分子间和分子内的非B-DNA构象，这些构象可能在生物过程中发挥重要作用。用核磁共振和X射线结晶学研究了端粒寡核苷酸dAGGG(TTAGGG)(3)的反平行和平行两种分子结构。在这两种结构中，端粒序列采用分子内四链结构，该结构由G-4四元组稳定，但序列折叠成四链的方式不同。人类端粒DNA的折叠被描述为反平行篮型和平行螺旋型。我们用~(125)I-放射性探针法测定了在Na~+或K~+离子存在的溶液中端粒四链的构象。I-125衰变引起DNA断裂的概率与放射性核素与DNA骨架糖单元之间的距离成反比，因此可以根据断裂的分布来推断DNA骨架的构象。将在Na+和K+存在下测得的断裂概率与由核磁共振和晶体结构获得的篮型和螺旋型四链的距离进行了比较。我们的放射性探测数据表明，在K+和Na+存在的情况下，溶液中存在反平行构象。在含Na+的溶液中，篮型反平行四链构象较好，而K+的存在有利于椅型反平行四链的构象。因此，我们认为溶液中可能存在两种反平行构象和平行构象，它们的相对比例取决于离子的类型和浓度。
A repeated non-coding DNA sequence d(TTAGGG)(n) is present in the telomeric ends of all human chromosomes. These repeats can adopt multiple inter and intramolecular non-B-DNA conformations that may play an important role in biological processes. Two intramolecular structures of the telomeric oligonucleotide dAGGG(TTAGGG)(3), antiparallel and parallel, have been solved by NMR and X-ray crystallography. In both structures, the telomeric sequence adopts an intramolecular quadruplex structure that is stabilized by G-4 quartets, but the ways in which the sequence folds into the quadruplex are different. The folds of the human telomeric DNA were described as an anti-parallel basket-type and a parallel propeller-type. We applied I-125-radioprobing to determine the conformation of the telomeric quadruplex in solution, in the presence of either Na+ or K+ ions. The probability of DNA breaks caused by decay of I-125 is inversely related to the distance between the radionuclide and the sugar unit of the DNA backbone; hence, the conformation of the DNA backbone can be deduced from the distribution of breaks. The probability of breaks measured in the presence of Na+ and K+ were compared with the distances in basket-type and propeller-type quadruplexes obtained from the NMR and crystal structures. Our radioprobing data demonstrate that the antiparallel conformation was present in solution in the presence of both K+ and Na+. The preferable conformation in the Na+-containing solution was the basket-type antiparallel quadruplex whereas the presence of K+ favored the chair-type antiparallel quadruplex. Thus, we believe that the two antiparallel and the parallel conformations may coexist in solution, and that their relative proportion is determined by the type and concentration of ions.