Souret Frédéric F, Kastenmayer James P, Green Pamela J
Delaware Biotechnology Institute, University of Delaware, Newark 19711, USA.
Mol Cell. 2004 Jul 23;15(2):173-83. doi: 10.1016/j.molcel.2004.06.006.
Messenger RNA degradation is an essential step in gene expression that can be regulated by siRNAs or miRNAs. However, most of our knowledge of in vivo eukaryotic mRNA degradation mechanisms derives from Saccharomyces cerevisiae, which lacks miRNAs and RNAi capability. Using reverse genetic and microarray analyses, we have identified multiple substrates of AtXRN4, the Arabidopsis homolog of the major yeast mRNA degrading exoribonuclease, Xrn1p. Insertional mutation of AtXRN4 leads to accumulation of the 3' end of several mRNAs, in a manner that correlates with increased stability of the 3' end, and is reversed following complementation with AtXRN4. Moreover, 3' products of miRNA-mediated cleavage of SCARECROW-LIKE transcripts and several other miRNA target transcripts are among those that accumulate in xrn4 mutants. The demonstration that an Xrn1p homolog degrades mRNA in a multicellular eukaryote and contributes to the miRNA-mediated decay pathway of selected targets has implications for XRNs in other organisms.
信使核糖核酸（mRNA）降解是基因表达中的一个重要步骤，可受到小分子干扰RNA（siRNA）或微小RNA（miRNA）的调控。然而，我们目前对于真核生物体内mRNA降解机制的了解大多源自酿酒酵母，而酿酒酵母缺乏miRNA和RNA干扰（RNAi）能力。通过反向遗传学和微阵列分析，我们鉴定出了AtXRN4的多个底物，AtXRN4是酵母主要的mRNA降解外切核糖核酸酶Xrn1p在拟南芥中的同源物。AtXRN4的插入突变导致几种mRNA的3'端积累，其积累方式与3'端稳定性增加相关，并且在与AtXRN4互补后这种积累现象会逆转。此外，miRNA介导的稻草人样转录本及其他几种miRNA靶转录本的切割产生的3'产物也在xrn4突变体中积累。在多细胞真核生物中，Xrn1p的同源物AtXRN4可降解mRNA并参与特定靶标的miRNA介导的降解途径，这一发现对其他生物体中的XRNs具有重要意义。
