Griffith J, Bianchi A, de Lange T
Lineberger Comprehensive Cancer Center, University of North Carolina at Chapel Hill, Chapel Hill, NC, 27599-7295, USA.
J Mol Biol. 1998 Apr 24;278(1):79-88. doi: 10.1006/jmbi.1998.1686.
Human telomeres consist of long arrays of TTAGGG repeats bound to the telomere-specific proteins, TRF1 and TRF2. Here we describe the structure of in vitro complexes formed between telomeric DNA and TRF1 as deduced by electron microscopy. Visualization of TRF1 bound to DNA containing six or 12 tandem TTAGGG repeats revealed a population of DNAs containing a spherical protein complex localized just to the repeats. Mass analysis of the protein complexes suggested binding of TRF1 dimers and tetramers to the TTAGGG repeats. The DNA was not significantly compacted or extended by protein binding. TRF1 formed filamentous structures on longer telomeric repeat arrays (>/=27 repeats) consistent with the presence of an array of bound TRF1 dimers. Unexpectedly, there was a strong propensity for two telomeric tracts to form paired synapses over the TRF1 covered segment. Up to 30% of the TRF1-bound DNAs could be found in a paired configuration with a strong bias for a parallel as contrasted to an antiparallel arrangement. TRF1-induced pairing was confirmed using a ligation assay which detected the formation of DNA multimers dependent on the presence of TRF1 and a 27mer repeat array in the DNA. These findings suggests that this protein may have an architectural role at telomeres. We discuss the possibility that TRF1-dependent changes in the conformation of telomeres are involved in the regulation of telomere length.
人类端粒由与端粒特异性蛋白TRF1和TRF2结合的TTAGGG重复序列长阵列组成。在此，我们描述了通过电子显微镜推断出的端粒DNA与TRF1之间形成的体外复合物的结构。观察与含有六个或十二个串联TTAGGG重复序列的DNA结合的TRF1，发现一群DNA含有仅定位于重复序列的球形蛋白复合物。对蛋白复合物的质量分析表明TRF1二聚体和四聚体与TTAGGG重复序列结合。蛋白质结合并未使DNA明显压缩或伸展。TRF1在较长的端粒重复序列阵列（≥27个重复序列）上形成丝状结构，这与一系列结合的TRF1二聚体的存在一致。出乎意料的是，在TRF1覆盖的片段上，两条端粒序列有很强的形成配对突触的倾向。在TRF1结合的DNA中，高达30%可以以配对形式存在，与反平行排列相比，强烈偏向于平行排列。使用连接试验证实了TRF1诱导的配对，该试验检测了依赖于TRF1和DNA中27聚体重复序列阵列的存在而形成的DNA多聚体。这些发现表明该蛋白可能在端粒处具有结构作用。我们讨论了端粒构象中依赖于TRF1的变化参与端粒长度调节的可能性。
