Newman A J, Norman C
MRC Laboratory of Molecular Biology, Cambridge, England.
Cell. 1992 Feb 21;68(4):743-54. doi: 10.1016/0092-8674(92)90149-7.
U5 snRNA is an essential pre-mRNA splicing factor whose function remains enigmatic. Specific mutations in a conserved single-stranded loop sequence in yeast U5 snRNA can activate cleavage of G1----A mutant pre-mRNAs at aberrant 5' splice sites and facilitate processing of dead-end lariat intermediates to mRNA. Activation of aberrant 5' cleavage sites involves base pairing between U5 snRNA and nucleotides upstream of the cleavage site. Processing of dead-end lariat intermediates to mRNA correlates with base pairing between U5 and the first two bases in exon 2. The loop sequence in U5 snRNA may therefore by intimately involved in the transesterification reactions at 5' and 3' splice sites. This pattern of interactions is strikingly reminiscent of exon recognition events in group II self-splicing introns and is consistent with the notion that U5 snRNA may be related to a specific functional domain from a group II-like self-splicing ancestral intron.
U5小核仁核糖核酸是一种必不可少的前体信使核糖核酸剪接因子，其功能仍然神秘莫测。酵母U5小核仁核糖核酸中保守单链环序列的特定突变，能够激活G1→A突变体前体信使核糖核酸在异常5'剪接位点的切割，并促进无活性套索状中间体加工成信使核糖核酸。异常5'切割位点的激活涉及U5小核仁核糖核酸与切割位点上游核苷酸之间的碱基配对。无活性套索状中间体加工成信使核糖核酸与U5和外显子2中前两个碱基之间的碱基配对相关。因此，U5小核仁核糖核酸中的环序列可能密切参与5'和3'剪接位点的转酯反应。这种相互作用模式惊人地让人联想到II类自我剪接内含子中的外显子识别事件，并且与U5小核仁核糖核酸可能与来自II类样自我剪接祖先内含子的特定功能域相关这一观点一致。
