Department of Biology, Stanford University, Stanford, CA 94305, USA.
Proc Natl Acad Sci U S A. 2010 Jul 20;107(29):12816-21. doi: 10.1073/pnas.1007580107. Epub 2010 Jun 28.
Various DNA sequences that interfere with transcription due to their unusual structural properties have been implicated in the regulation of gene expression and with genomic instability. An important example is sequences containing G-rich homopurine-homopyrimidine stretches, for which unusual transcriptional behavior is implicated in regulation of immunogenesis and in other processes such as genomic translocations and telomere function. To elucidate the mechanism of the effect of these sequences on transcription we have studied T7 RNA polymerase transcription of G-rich sequences in vitro. We have shown that these sequences produce significant transcription blockage in an orientation-, length- and supercoiling-dependent manner. Based upon the effects of various sequence modifications, solution conditions, and ribonucleotide substitutions, we conclude that transcription blockage is due to formation of unusually stable RNA/DNA hybrids, which could be further exacerbated by triplex formation. These structures are likely responsible for transcription-dependent replication blockage by G-rich sequences in vivo.
由于其异常的结构特性而干扰转录的各种 DNA 序列已被牵涉到基因表达的调控和基因组不稳定性中。一个重要的例子是含有富含 G 的同聚嘌呤-同聚嘧啶链的序列，其异常的转录行为与免疫发生的调节以及其他过程（如基因组易位和端粒功能）有关。为了阐明这些序列对转录的影响机制，我们已经在体外研究了 T7 RNA 聚合酶对富含 G 的序列的转录。我们已经表明，这些序列以取向、长度和超螺旋依赖的方式产生显著的转录阻断。基于各种序列修饰、溶液条件和核糖核苷酸取代的影响，我们得出结论，转录阻断是由于形成了异常稳定的 RNA/DNA 杂交体，这可能会因三链体形成而进一步加剧。这些结构可能是富含 G 的序列在体内引起依赖于转录的复制阻断的原因。
