Jumaa H, Nielsen P J
Max Planck Institute for Immunobiology, Stuebeweg 51, D-79108, i. Br, Freiburg, Germany.
Biochim Biophys Acta. 2000 Nov 15;1494(1-2):137-43. doi: 10.1016/s0167-4781(00)00233-5.
SR proteins are essential splicing factors involved in the use of both constitutive and alternative exons. We previously showed that the SR proteins SRp20 and ASF/SF2 have antagonistic activities on SRp20 pre-mRNA splicing. SRp20 activates exon 4 recognition in its pre-mRNA, whereas ASF/SF2 inhibits this recognition. In experiments aimed at testing the specificity of SRp20 and ASF/SF2 for exon 4 splicing regulation, we show here that this specificity lies in the RNA binding domains of SRp20 and ASF/SF2 and not in the RS domains. Surprisingly, a deletion of 14 amino acids at the end of ASF/SF2-RBD2 converts ASF/SF2 from an inhibitor to an activator of exon 4 splicing. We found that ASF3 also inhibits exon 4 recognition, thus acting similarly to ASF/SF2, while SC35 activates a cryptic 5' splice site downstream of exon 3 and, in doing so, represses exon 4 use. In contrast, Tra2 and the SR proteins 9G8 and SRp40 do not appear to affect exon 4 splicing.
SR蛋白是参与组成型外显子和可变外显子剪接的重要剪接因子。我们之前表明，SR蛋白SRp20和ASF/SF2对SRp20前体mRNA剪接具有拮抗活性。SRp20可激活其前体mRNA中外显子4的识别，而ASF/SF2则抑制这种识别。在旨在测试SRp20和ASF/SF2对外显子4剪接调控特异性的实验中，我们在此表明这种特异性存在于SRp20和ASF/SF2的RNA结合结构域中，而非RS结构域。令人惊讶的是，ASF/SF2-RBD2末端缺失14个氨基酸会使ASF/SF2从外显子4剪接的抑制剂转变为激活剂。我们发现ASF3也抑制外显子4的识别，因此其作用与ASF/SF2类似，而SC35激活外显子3下游的一个隐蔽5'剪接位点，这样做会抑制外显子4的使用。相比之下，Tra2以及SR蛋白9G8和SRp40似乎不影响外显子4的剪接。
