Département de Biochimie, Faculté de Médecine et des Sciences de la Santé, Pavillon de Recherche Appliquée au Cancer, Université de Sherbrooke, Québec, Canada J1E 4K8.
RNA. 2014 Jul;20(7):1129-41. doi: 10.1261/rna.044578.114. Epub 2014 May 27.
G-quadruplexes are widespread four-stranded structures that are adopted by G-rich regions of both DNA and RNA and are involved in essential biological processes such as mRNA translation. They are formed by the stacking of two or more G-quartets that are linked together by three loops. Although the maximal loop length is usually fixed to 7 nt in most G-quadruplex-predicting software, it has already been demonstrated that artificial DNA G-quadruplexes containing two distal loops that are limited to 1 nt each and a central loop up to 30 nt long are likely to form in vitro. This report demonstrates that such structures possessing a long central loop are actually found in the 5'-UTRs of human mRNAs. Firstly, 1453 potential G-quadruplex-forming sequences (PG4s) were identified through a bioinformatic survey that searched for sequences respecting the requirement for two 1-nt long distal loops and a long central loop of 2-90 nt in length. Secondly, in vitro in-line probing experiments confirmed and characterized the folding of eight candidates possessing central loops of 10-70 nt long. Finally, the biological effect of several G-quadruplexes with a long central loop on mRNA expression was studied in cellulo using a luciferase gene reporter assay. Clearly, the actual definition of G-quadruplex-forming sequences is too conservative and must be expanded to include the long central loop. This greatly expands the number of expected PG4s in the transcriptome. Consideration of these new candidates might aid in elucidating the potentially important biological implications of the G-quadruplex structure.
四链体是广泛存在的四链结构，存在于 DNA 和 RNA 的富含 G 区域，并参与如 mRNA 翻译等重要的生物学过程。它们由两个或多个 G-四联体通过三个环连接而成。尽管大多数 G-四联体预测软件通常将最大环长度固定为 7nt，但已经证明含有两个远端环（每个环长度限制为 1nt）和一个中央环（长度可达 30nt）的人工 DNA G-四联体很可能在体外形成。本报告表明，实际上这种具有长中央环的结构存在于人类 mRNA 的 5'UTR 中。首先，通过生物信息学调查，搜索了满足两个 1nt 长远端环和一个 2-90nt 长中央环要求的序列，鉴定了 1453 个潜在的 G-四联体形成序列（PG4s）。其次，体外在线探测实验证实并表征了 8 个具有 10-70nt 长中央环的候选物的折叠情况。最后，使用荧光素酶基因报告基因测定法在细胞内研究了几个具有长中央环的 G-四联体对 mRNA 表达的生物学影响。显然，G-四联体形成序列的实际定义过于保守，必须扩展到包括长中央环。这大大增加了转录组中预期的 PG4s 数量。考虑这些新的候选物可能有助于阐明 G-四联体结构的潜在重要生物学意义。
