Gaur R K, Valcárcel J, Green M R
Howard Hughes Medical Institute Program in Molecular Medicine, University of Massachusetts Medical Center, Worcester 01605, USA.
RNA. 1995 Jun;1(4):407-17.
Splicing of pre-mRNAs occurs via a lariat intermediate in which an intronic adenosine, embedded within a branch point sequence, forms a 2',5'-phosphodiester bond (RNA branch) with the 5' end of the intron. How the branch point is recognized and activated remains largely unknown. Using site-specific photochemical cross-linking, we have identified two proteins that specifically interact with the branch point during the splicing reaction. U2AF65, an essential splicing factor that binds to the adjacent polypyrimidine tract, crosslinks to the branch point at the earliest stage of spliceosome formation in an ATP-independent manner. A novel 28-kDa protein, which is a constituent of the mature spliceosome, contacts the branch point after the first catalytic step. Our results indicate that the branch point is sequentially recognized by distinct splicing factors in the course of the splicing reaction.
前体mRNA的剪接通过套索状中间体进行，其中嵌入分支点序列中的内含子腺苷与内含子的5'端形成2',5'-磷酸二酯键（RNA分支）。分支点是如何被识别和激活的，在很大程度上仍然未知。利用位点特异性光化学交联技术，我们鉴定出了两种在剪接反应过程中与分支点特异性相互作用的蛋白质。U2AF65是一种必需的剪接因子，它与相邻的多嘧啶序列结合，在剪接体形成的最早阶段以不依赖ATP的方式与分支点发生交联。一种新型的28 kDa蛋白质是成熟剪接体的组成成分，在第一步催化反应后与分支点接触。我们的结果表明，在剪接反应过程中，分支点被不同的剪接因子依次识别。
