Patel Snehal Bhikhu, Novikova Natalya, Bellini Michel
Department of Biochemistry, College of Medicine, School of Molecular and Cellular Biology, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA.
J Cell Biol. 2007 Sep 10;178(6):937-49. doi: 10.1083/jcb.200706134.
In amphibian oocytes, most lateral loops of the lampbrush chromosomes correspond to active transcriptional sites for RNA polymerase II. We show that newly assembled small nuclear ribonucleoprotein (RNP [snRNP]) particles, which are formed upon cytoplasmic injection of fluorescently labeled spliceosomal small nuclear RNAs (snRNAs), target the nascent transcripts of the chromosomal loops. With this new targeting assay, we demonstrate that nonfunctional forms of U1 and U2 snRNAs still associate with the active transcriptional units. In particular, we find that their association with nascent RNP fibrils is independent of their base pairing with pre-messenger RNAs. Additionally, stem loop I of the U1 snRNA is identified as a discrete domain that is both necessary and sufficient for association with nascent transcripts. Finally, in oocytes deficient in splicing, the recruitment of U1, U4, and U5 snRNPs to transcriptional units is not affected. Collectively, these data indicate that the recruitment of snRNPs to nascent transcripts and the assembly of the spliceosome are uncoupled events.
在两栖类卵母细胞中，灯刷染色体的大多数侧环对应于RNA聚合酶II的活跃转录位点。我们发现，通过向细胞质中注射荧光标记的剪接体小核RNA（snRNA）而新组装形成的小核核糖核蛋白（RNP [snRNP]）颗粒，会靶向染色体环的新生转录本。利用这种新的靶向检测方法，我们证明了U1和U2 snRNA的无功能形式仍与活跃转录单元相关联。特别是，我们发现它们与新生RNP纤维的关联独立于它们与前体信使RNA的碱基配对。此外，U1 snRNA的茎环I被确定为一个离散结构域，它对于与新生转录本的关联既是必要的也是充分的。最后，在剪接缺陷的卵母细胞中，U1、U4和U5 snRNP向转录单元的募集不受影响。总体而言，这些数据表明snRNP向新生转录本的募集和剪接体的组装是不相关的事件。
