Specific phosphorylation of SR proteins by mammalian DNA topoisomerase I
Specific phosphorylation of SR proteins by mammalian DNA topoisomerase I
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DOI：
10.1038/381080a0
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发表时间：
1996-05-02
期刊：
影响因子：
64.8
通讯作者：
Tazi, J
中科院分区：
文献类型：
--
作者：
Rossi, F;Labourier, E;Tazi, J
几种后生动物剪接因子的特征在于核糖核蛋白（RNP）共有序列和丝氨酸-丝氨酸重复序列（RS结构域）（1-8），这对于它们在剪接中的功能是必需的（5，9，10）。这些包括SR蛋白家族（SC 35，SF 2/ASF），U1小核（sn）RNP蛋白（U1- 70 K）和U2 snRNP辅助因子（U2 AF）的成员。SR蛋白在体内被磷酸化（11），并且U1- 70 K的RS结构域的磷酸化状态影响其剪接活性（12）。在这里，我们报告的蛋白激酶的纯化，是特定的SR蛋白，并表明它是DNA拓扑异构酶I。这种酶缺乏典型的ATP结合基序，但以50 nM的解离常数阻碍ATP。喜树碱及其衍生物是DNA拓扑异构酶I的特异性抑制剂，在DNA存在下强烈抑制激酶活性并影响SR蛋白的磷酸化状态。因此，DNA拓扑异构酶I很可能是在体内工作的SR蛋白激酶之一。
SEVERAL metazoan splicing factors are characterized by ribonucleoprotein (RNP) consensus sequences and arginine-serine repeats (RS domain)(1-8) which are essential for their function in splicing(5,9,10). These include members of the SR-protein family (SC35, SF2/ASF), the U1 small nuclear (sn)RNP protein (U1-70K) and the U2 snRNP auxiliary factor (U2AF). SR proteins are phosphorylated in vivo(11) and the phosphorylation state of U1-70K's RS domain influences its splicing activity(12). Here we report the purification of a protein kinase that is specific for SR proteins and show that it is DNA topoisomerase I. This enzyme lacks a canonical ATP-binding motif hut hinds ATP with a dissociation constant of 50 nM. Camptothecin and derivatives, known to be specific inhibitors of DNA topoisomerase I, strongly inhibit the kinase activity in the presence of DNA and affect the phosphorylation state of SR proteins. Thus, DNA topoisomerase I may well be one of the SR protein kinases operating in vivo.