Simpson C G, Brown J W S
Scottish Crop Research Institute, Invergowrie, Dundee Scotland, UK.
Curr Top Microbiol Immunol. 2008;326:61-82. doi: 10.1007/978-3-540-76776-3_4.
U12-dependent (U12) introns have persisted in the genomes of plants since the ancestral divergence between plants and metazoans. These introns, which are rare, are found in a range of genes that include essential functions in DNA replication and RNA metabolism and are implicated in regulating the expression of their host genes. U12 introns are removed from pre-mRNAs by a U12 intron-specific spliceosome. Although this spliceosome shares many properties with the more abundant U2-dependent (U2) intron spliceosome, four of the five small nuclear RNAs (snRNAs) required for splicing are different and specific for the unique splicing of U12 introns. Evidence in plants so far indicates that splicing signals of plant U12 introns and their splicing machinery are similar to U12 intron splicing in other eukaryotes. In addition to the high conservation of splicing signals, plant U12 introns also retain unique characteristic features of plant U2 introns, such as UA-richness, which suggests a requirement for plant-specific components for both the U2 and U12 splicing reaction. This chapter compares U12 and U2 splicing and reviews what is known about plant U12 introns and their possible role in gene expression.
自植物与后生动物在进化上分化以来，依赖U12的（U12）内含子一直存在于植物基因组中。这些内含子较为罕见，存在于一系列基因中，这些基因在DNA复制和RNA代谢中具有重要功能，并参与调控其宿主基因的表达。U12内含子通过U12内含子特异性剪接体从前体mRNA中去除。虽然这种剪接体与更为常见的依赖U2的（U2）内含子剪接体有许多共同特性，但剪接所需的五个小核RNA（snRNA）中有四个不同，且对U12内含子的独特剪接具有特异性。目前植物中的证据表明，植物U12内含子的剪接信号及其剪接机制与其他真核生物中的U12内含子剪接相似。除了剪接信号的高度保守性外，植物U12内含子还保留了植物U2内含子的独特特征，如富含UA，这表明U2和U12剪接反应都需要植物特异性成分。本章比较了U12和U2剪接，并综述了关于植物U12内含子及其在基因表达中可能作用的已知信息。
