Bacíková Dagmar, Horowitz David S
Department of Biochemistry and Molecular Biology, Uniformed Services University of the Health Sciences, 4301 Jones Bridge Rd., Bethesda, MD 20814, USA.
Mol Cell Biol. 2005 Mar;25(6):2107-16. doi: 10.1128/MCB.25.6.2107-2116.2005.
Both the Prp18 protein and the U5 snRNA function in the second step of pre-mRNA splicing. We identified suppressors of mutant prp18 alleles in the gene for the U5 snRNA (SNR7). The suppressors' U5 snRNAs have either a U4-to-A or an A8-to-C mutation in the evolutionarily invariant loop 1 of U5. Suppression is specific for prp18 alleles that encode proteins with mutations in a highly conserved region of Prp18 which forms an unstructured loop in crystals of Prp18. The snr7 suppressors partly restored the pre-mRNA splicing activity that was lost in the prp18 mutants. The close functional relationship of Prp18 and U5 is emphasized by the finding that two snr7 alleles, U5A and U6A, are dominant synthetic lethal with prp18 alleles. Our results support the idea that Prp18 and the U5 snRNA act in concert during the second step of pre-mRNA splicing and suggest a model in which the conserved loop of Prp18 acts to stabilize the interaction of loop 1 of the U5 snRNA with the splicing intermediates.
Prp18蛋白和U5 snRNA都在mRNA前体剪接的第二步发挥作用。我们在U5 snRNA（SNR7）基因中鉴定出了突变prp18等位基因的抑制子。这些抑制子的U5 snRNAs在U5进化上保守的环1中有一个U4到A或A8到C的突变。抑制作用对编码在Prp18高度保守区域发生突变的蛋白质的prp18等位基因具有特异性，该区域在Prp18晶体中形成一个无结构的环。snr7抑制子部分恢复了prp18突变体中丧失的mRNA前体剪接活性。两个snr7等位基因U5A和U6A与prp18等位基因是显性合成致死的，这一发现强调了Prp18和U5之间密切的功能关系。我们的结果支持了Prp18和U5 snRNA在mRNA前体剪接第二步协同作用的观点，并提出了一个模型，其中Prp18的保守环起到稳定U5 snRNA环1与剪接中间体相互作用的作用。
