Orum H, Nielsen H, Engberg J
Department of Biochemistry B, University of Copenhagen, Denmark.
J Mol Biol. 1991 Nov 20;222(2):219-32. doi: 10.1016/0022-2836(91)90208-n.
We have identified and characterized the full set of spliceosomal small nuclear RNAs (snRNAs; U1, U2, U4, U5 and U6) from the ciliated protozoan Tetrahymena thermophila. With the exception of U4 snRNA, the sizes of the T. thermophila snRNAs are closely similar to their metazoan homologues. The T. thermophila snRNAs all have unique 5' ends, which start with an adenine residue. In contrast, with the exception of U6, their 3' ends show some size heterogeneity. The primary sequences of the T. thermophila snRNAs contain the sequence motifs shown, or proposed, to be of functional importance in other organisms. Furthermore, secondary structures closely similar to phylogenetically proven models can be inferred from the T. thermophila data. Analysis of the snRNA sequences identifies three potential snRNA-snRNA base-pairing interactions, all of which are consistent with available phylogenetic data. Two of these occur between U2 and U6, whereas the third occurs between U1 and U2. The proposed interactions locate the intron 5' splice-site close to the intron branch-site nucleotide as well as to the most highly conserved domain of U6. We envisage that these interactions may facilitate the first step of pre-mRNA splicing.
我们已经鉴定并表征了来自纤毛原生动物嗜热栖热四膜虫的全套剪接体小核RNA（snRNA；U1、U2、U4、U5和U6）。除U4 snRNA外，嗜热栖热四膜虫snRNA的大小与它们后生动物的同源物非常相似。嗜热栖热四膜虫的snRNA都有独特的5'端，以腺嘌呤残基开始。相比之下，除U6外，它们的3'端显示出一些大小异质性。嗜热栖热四膜虫snRNA的一级序列包含已显示或被认为在其他生物体中具有功能重要性的序列基序。此外，从嗜热栖热四膜虫的数据可以推断出与系统发育证实的模型非常相似的二级结构。对snRNA序列的分析确定了三种潜在的snRNA-snRNA碱基配对相互作用，所有这些都与现有的系统发育数据一致。其中两种发生在U2和U6之间，而第三种发生在U1和U2之间。所提出的相互作用将内含子5'剪接位点定位在内含子分支位点核苷酸附近以及U6的最高度保守结构域附近。我们设想这些相互作用可能有助于前体mRNA剪接的第一步。
