Achsel T, Shimura Y
Department of Biophysics, Faculty of Science, Kyoto University.
J Biochem. 1996 Jul;120(1):53-60. doi: 10.1093/oxfordjournals.jbchem.a021393.
The excision of introns with weak polypyrimidine tracts at their 3' splice sites can be enhanced by sequence elements in the downstream exon or by a downstream 5' splice site. The enhancers inside the exon do not conform to a strict consensus, but they are generally rich in purines. Here, we show that members of the family of SR proteins recognize these elements. Not only does SF2/ASF activate many different polypurine enhancers, but also at least one other SR protein, most likely SC35, is active as well. The degree of splicing activation varies with the polypurine enhancers and the SR proteins. Further, we show that the similar activation by downstream 5' splice sites requires U1 snRNP, which is not the case with purine-rich enhancers. These results are consistent with a model showing that U1 snRNP binds to the 5' splice site and SR proteins to exonic sequences upstream of the 5' splice site. Both interact with U2AF at the 3' splice site. This represents a molecular explanation for the exon recognition which is important for splice site selection in mammals.
在其3'剪接位点具有弱嘧啶富集区的内含子的切除可通过下游外显子中的序列元件或下游5'剪接位点来增强。外显子内部的增强子并不符合严格的共有序列，但它们通常富含嘌呤。在这里，我们表明SR蛋白家族的成员识别这些元件。不仅SF2/ASF激活许多不同的多嘌呤增强子，而且至少一种其他SR蛋白，很可能是SC35，也具有活性。剪接激活的程度因多嘌呤增强子和SR蛋白而异。此外，我们表明下游5'剪接位点的类似激活需要U1 snRNP，而富含嘌呤的增强子则不然。这些结果与一个模型一致，该模型表明U1 snRNP结合到5'剪接位点，而SR蛋白结合到5'剪接位点上游的外显子序列。两者都在3'剪接位点与U2AF相互作用。这代表了对哺乳动物剪接位点选择中重要的外显子识别的分子解释。
