Lockhart S R, Rymond B C
T. H. Morgan School of Biological Sciences, University of Kentucky, Lexington 40506-0225.
Mol Cell Biol. 1994 Jun;14(6):3623-33. doi: 10.1128/mcb.14.6.3623-3633.1994.
The binding of a U1 small nuclear ribonucleoprotein (snRNP) particle to the 5' splice site region of a pre-mRNA is a primary step of intron recognition. In this report, we identify a novel 75-kDa polypeptide of Saccharomyces cerevisiae, Prp39p, necessary for the stable interaction of mRNA precursors with the snRNP components of the pre-mRNA splicing machinery. In vivo, temperature inactivation or metabolic depletion of Prp39p blocks pre-mRNA splicing and causes growth arrest. Analyses of cell extracts reveal a specific and dramatic increase in the electrophoretic mobility of the U1 snRNP particle upon Prp39p depletion and demonstrate that extracts deficient in Prp39p activity are unable to form either the CC1 or CC2 commitment complex band characteristic of productive U1 snRNP/pre-mRNA association. Immunological studies establish that Prp39p is uniquely associated with the U1 snRNP and is recruited with the U1 snRNP into splicing complexes. On the basis of these and related observations, we propose that Prp39p functions, at least in part, prior to stable branch point recognition by the U1 snRNP particle to facilitate or stabilize the U1 snRNP/5' splice site interaction.
U1小核核糖核蛋白（snRNP）颗粒与前体mRNA的5'剪接位点区域结合是内含子识别的首要步骤。在本报告中，我们鉴定出酿酒酵母中一种新的75 kDa多肽Prp39p，它对于mRNA前体与前体mRNA剪接机制的snRNP组分的稳定相互作用是必需的。在体内，Prp39p的温度失活或代谢消耗会阻断前体mRNA剪接并导致生长停滞。对细胞提取物的分析显示，Prp39p缺失时U1 snRNP颗粒的电泳迁移率会有特异性且显著的增加，并表明缺乏Prp39p活性的提取物无法形成有活性的U1 snRNP/前体mRNA结合所特有的CC1或CC2起始复合物条带。免疫学研究证实Prp39p仅与U1 snRNP相关，并与U1 snRNP一起被招募到剪接复合物中。基于这些及相关观察结果，我们提出Prp39p至少部分在U1 snRNP颗粒稳定识别分支点之前发挥作用，以促进或稳定U1 snRNP/5'剪接位点的相互作用。
