Halder Kangkan, Wieland Markus, Hartig Jörg S
Department of Chemistry, Konstanz Research School Chemical Biology and Zukunftskolleg, University of Konstanz, Universitätsstr 10, 78457 Konstanz, Germany.
Nucleic Acids Res. 2009 Nov;37(20):6811-7. doi: 10.1093/nar/gkp696. Epub 2009 Sep 9.
Four-stranded DNA and RNA quadruplexes or G4 motifs are non-B DNA conformations that are presumed to form in vivo, although only few explicit evidence has been reported. Using bioinformatics the presence of putative DNA G-quadruplexes within critical promoter regions has been demonstrated and a regulatory role in transcription has been suspected. However, in genomic DNA the presence of the complementary strand interferes with the potential to form a quadruplex motif. Contrarily RNA G4 motifs have no such limitation and consequently strong interference with gene expression is suspected. Nevertheless, experimental evidence is scarce. Here we show a well-defined structure-function relationship of synthetic quadruplex sequences in 5'-UTRs in multiple mammalian cell-lines. We establish a universal 'translational suppressor' effect of these motifs on gene expression at the translational level and show for the first time that specific features such as loop-length and the number of 'GGG'-repeats further determine the suppressive impact. Moreover, a consistent and predictable repression of gene expression is observed for naturally occurring RNA G4 motifs, augmenting the functional relevance of these unusual nucleic acid structures.
四链DNA和RNA四链体或G4基序是非B型DNA构象，尽管仅有少量确切证据被报道，但推测其在体内形成。通过生物信息学方法，已证实关键启动子区域内存在假定的DNA G-四链体，并怀疑其在转录中具有调控作用。然而，在基因组DNA中，互补链的存在会干扰形成四链体基序的可能性。相反，RNA G4基序没有这种限制，因此怀疑其对基因表达有强烈干扰。尽管如此，实验证据仍然稀少。在这里，我们展示了多种哺乳动物细胞系5'-非翻译区（5'-UTR）中合成四链体序列明确的结构-功能关系。我们在翻译水平上建立了这些基序对基因表达的普遍“翻译抑制”作用，并首次表明诸如环长度和“GGG”重复次数等特定特征进一步决定了抑制作用的程度。此外，对于天然存在的RNA G4基序，观察到基因表达的一致且可预测的抑制作用，增强了这些异常核酸结构的功能相关性。
