Jackson S P, MacDonald J J, Lees-Miller S, Tjian R
Howard Hughes Medical Institute, Department of Molecular and Cell Biology, University of California, Berkeley 94720.
Cell. 1990 Oct 5;63(1):155-65. doi: 10.1016/0092-8674(90)90296-q.
Efficient transcription of SV40 early genes requires transcription factor Sp1. Here, we report that SV40 infection induces Sp1 phosphorylation. While characterizing this modification, we discovered that Sp1 becomes quantitatively phosphorylated in an in vitro transcription extract. Multiple processive phosphorylation of Sp1 depends on binding of Sp1 to GC box-containing DNA. Cell fractionation and column chromatography reveal that the Sp1 kinase is a nuclear DNA binding protein that corresponds to a previously identified DNA-dependent protein kinase. Because only some trans-activators are phosphorylated by this kinase, Sp1 belongs to a specific subgroup of factors that are phosphorylated upon binding to promoter sequences. Finally, efficient phosphorylation of Sp1 requires both a functional DNA binding domain and a region containing the transcriptional activation domains. Coupling of phosphorylation to DNA binding may represent a novel mechanism for regulating transcriptional initiation.
SV40早期基因的有效转录需要转录因子Sp1。在此，我们报告SV40感染会诱导Sp1磷酸化。在对这种修饰进行表征时，我们发现Sp1在体外转录提取物中会发生定量磷酸化。Sp1的多次持续性磷酸化依赖于Sp1与含GC盒的DNA的结合。细胞分级分离和柱色谱分析表明，Sp1激酶是一种核DNA结合蛋白，与先前鉴定的DNA依赖性蛋白激酶相对应。由于只有一些反式激活因子会被这种激酶磷酸化，Sp1属于在与启动子序列结合后被磷酸化的特定因子亚组。最后，Sp1的有效磷酸化既需要功能性DNA结合结构域，也需要包含转录激活结构域的区域。磷酸化与DNA结合的偶联可能代表了一种调节转录起始的新机制。
