Kroeger Tiffany S, Watkins Kenneth P, Friso Giulia, van Wijk Klaas J, Barkan Alice
Institute of Molecular Biology, University of Oregon, Eugene, OR 97403, USA.
Proc Natl Acad Sci U S A. 2009 Mar 17;106(11):4537-42. doi: 10.1073/pnas.0812503106. Epub 2009 Feb 26.
Comparative genomics has provided evidence for numerous conserved protein domains whose functions remain unknown. We identified a protein harboring "domain of unknown function 860" (DUF860) as a component of group II intron ribonucleoprotein particles in maize chloroplasts. This protein, assigned the name WTF1 ("what's this factor?"), coimmunoprecipitates from chloroplast extract with group II intron RNAs, is required for the splicing of the introns with which it associates, and promotes splicing in the context of a heterodimer with the RNase III-domain protein RNC1. Both WTF1 and its resident DUF860 bind RNA in vitro, demonstrating that DUF860 is a previously unrecognized RNA-binding domain. DUF860 is found only in plants, where it is represented in a protein family comprising 14 orthologous groups in angiosperms. Most members of the DUF860 family are predicted to localize to chloroplasts or mitochondria, suggesting that proteins with this domain have multiple roles in RNA metabolism in both organelles. These findings add to emerging evidence that the coevolution of nuclear and organellar genomes spurred the evolution of diverse noncanonical RNA-binding motifs that perform organelle-specific functions.
比较基因组学已为众多功能未知的保守蛋白质结构域提供了证据。我们鉴定出一种含有“未知功能结构域860”（DUF860）的蛋白质，它是玉米叶绿体中II类内含子核糖核蛋白颗粒的一个组成部分。这种蛋白质被命名为WTF1（“这是什么因子？”），它能从叶绿体提取物中与II类内含子RNA进行共免疫沉淀，是与其相关的内含子剪接所必需的，并且在与核糖核酸酶III结构域蛋白RNC1形成异二聚体的情况下促进剪接。WTF1及其所含的DUF860在体外均能结合RNA，这表明DUF860是一个此前未被识别的RNA结合结构域。DUF860仅在植物中发现，在被子植物中它存在于一个由14个直系同源组组成的蛋白质家族中。DUF860家族的大多数成员预计定位于叶绿体或线粒体，这表明具有该结构域的蛋白质在这两个细胞器的RNA代谢中具有多种作用。这些发现进一步证明，核基因组和细胞器基因组的共同进化推动了多种执行细胞器特异性功能的非经典RNA结合基序的进化。
