Martick Monika, Horan Lucas H, Noller Harry F, Scott William G
Center for Molecular Biology of RNA, University of California, Santa Cruz, California 95064, USA.
Nature. 2008 Aug 14;454(7206):899-902. doi: 10.1038/nature07117. Epub 2008 Jul 9.
Structured RNAs embedded in the untranslated regions (UTRs) of messenger RNAs can regulate gene expression. In bacteria, control of a metabolite gene is mediated by the self-cleaving activity of a ribozyme embedded in its 5' UTR. This discovery has raised the question of whether gene-regulating ribozymes also exist in eukaryotic mRNAs. Here we show that highly active hammerhead ribozymes are present in the 3' UTRs of rodent C-type lectin type II (Clec2) genes. Using a hammerhead RNA motif search with relaxed delimitation of the non-conserved regions, we detected ribozyme sequences in which the invariant regions, in contrast to the previously identified continuous hammerheads, occur as two fragments separated by hundreds of nucleotides. Notably, a fragment pair can assemble to form an active hammerhead ribozyme structure between the translation termination and the polyadenylation signals within the 3' UTR. We demonstrate that this hammerhead structure can self-cleave both in vitro and in vivo, and is able to reduce protein expression in mouse cells. These results indicate that an unrecognized mechanism of post-transcriptional gene regulation involving association of discontinuous ribozyme sequences within an mRNA may be modulating the expression of several CLEC2 proteins that function in bone remodelling and the immune response of several mammals.
嵌入信使核糖核酸（mRNA）非翻译区（UTR）的结构化核糖核酸（RNA）能够调控基因表达。在细菌中，代谢物基因的调控是由嵌入其5'UTR的核酶的自我切割活性介导的。这一发现引发了一个问题，即基因调控核酶是否也存在于真核生物的mRNA中。在这里，我们表明，高活性的锤头状核酶存在于啮齿动物C型凝集素II型（Clec2）基因的3'UTR中。使用对非保守区域进行宽松界定的锤头状RNA基序搜索，我们检测到了核酶序列，其中与先前鉴定的连续锤头状结构不同，保守区域以被数百个核苷酸隔开的两个片段形式出现。值得注意的是，一对片段可以组装形成一个活性锤头状核酶结构，位于3'UTR内的翻译终止信号和聚腺苷酸化信号之间。我们证明，这种锤头状结构在体外和体内都能自我切割，并且能够降低小鼠细胞中的蛋白质表达。这些结果表明，一种未被认识的转录后基因调控机制，涉及mRNA内不连续核酶序列的结合，可能正在调节几种参与多种哺乳动物骨重塑和免疫反应的Clec2蛋白的表达。
