Champion-Arnaud P, Reed R
Department of Cell Biology, Harvard Medical School, Boston, Massachusetts 02115.
Genes Dev. 1994 Aug 15;8(16):1974-83. doi: 10.1101/gad.8.16.1974.
The mammalian spliceosome-associated protein, SAP 49, is associated specifically with U2 snRNP and is the most efficiently UV cross-linked protein in the spliceosomal complexes A, B, and C. We show here that SAP 49 cross-links to a region in the pre-mRNA immediately upstream of the branchpoint sequence in the prespliceosomal complex A. In addition to the RNA-binding activity of SAP 49, we show that this protein interacts directly and highly specifically with another U2 snRNP-associated spliceosomal protein, SAP 145. We have isolated a cDNA-encoding SAP 49 and find that it contains two amino-terminal RNA-recognition motifs (RRMs), consistent with the observation that SAP 49 binds directly to pre-mRNA. The remainder of the protein is highly proline-glycine rich (39% proline and 17% glycine). Unexpectedly, the SAP 49-SAP 145 protein-protein interaction requires the amino-terminus of SAP 49 that contains the two RRMs. The observation that SAP 49 and SAP 145 interact directly with both U2 snRNP and the pre-mRNA suggests that this protein complex plays a role in tethering U2 snRNP to the branch site.
哺乳动物剪接体相关蛋白SAP 49，特异性地与U2 snRNP相关联，并且是剪接体复合物A、B和C中紫外线交联效率最高的蛋白。我们在此表明，在剪接体前体复合物A中，SAP 49与前体mRNA中分支点序列上游紧邻的区域发生交联。除了SAP 49的RNA结合活性外，我们还表明该蛋白直接且高度特异性地与另一种U2 snRNP相关的剪接体蛋白SAP 145相互作用。我们分离出了编码SAP 49的cDNA，发现它含有两个氨基末端RNA识别基序（RRMs），这与SAP 49直接结合前体mRNA的观察结果一致。该蛋白的其余部分富含脯氨酸和甘氨酸（脯氨酸占39%，甘氨酸占17%）。出乎意料的是，SAP 49与SAP 145的蛋白质 - 蛋白质相互作用需要含有两个RRMs的SAP 49的氨基末端。SAP 49和SAP 145都直接与U2 snRNP和前体mRNA相互作用这一观察结果表明，这种蛋白质复合物在将U2 snRNP拴系到分支位点中起作用。
