Douville P, Hagmann M, Georgiev O, Schaffner W
Institut für Molekularbiologie II, Universität Zürich, Switzerland.
Virology. 1995 Feb 20;207(1):107-16. doi: 10.1006/viro.1995.1056.
The control of the ICP0 and ICP4 immediate early genes of herpes simplex virus (HSV) can critically determine the course of viral lytic or latent infections. Their promoters contain so-called TAATGARAT motifs that are activated via a multiprotein complex which includes cellular proteins Oct-1 and HCF and the viral activator (VP16 (= Vmw65, alpha TIF). Relative to the ICP4 promoter TAATGAGAT sequence, the ICP0 promoter motif has a 5' extension that includes a full octamer sequence (ATGCTAATGATAT). It seemed possible that this overlapping octamer site might render the ICP0 promoter element more active by allowing tighter binding of the Oct-1/VP16 complex or more vulnerable to repression by other Oct proteins. Our experiments favor the former possibility. On the one hand, the extended ICP0 site shows stronger binding of the Oct-1/VP16 complex compared to the ICP4 site. Moreover, transcription of a reporter gene with multiple ICP0 sites is strongly activated by VP16 in transfected cells. On the other hand, the ICP0 site is largely refractory toward repression by a different Oct factor (N-Oct2 = Brn1) which competes with Oct-1/VP16 for the site. In marked contrast, multiple copies of the conventional TAATGAGAT motif of ICP4 are poorly activated by VP16, and transcription from this site can be completely repressed by N-Oct2. However, inclusion of the neighboring CGGAAR motifs from the ICP4 promoter, which bind factors GABP alpha and beta, results in a strong synergistic activation. This activity, like that of the complete ICP4 promoter, becomes refractory to repression by competing N-Oct2. Thus the standard TAATGARAT motif of ICP4 is by itself less active and more vulnerable to repression than the extended ICP0 motif, and its activation depends upon synergism with neighboring DNA sites and their cognate factors. This difference between the two types of TAATGARAT motifs may allow for a more complex transcriptional regulation by factor combinations.
单纯疱疹病毒（HSV）的ICP0和ICP4立即早期基因的调控对病毒裂解性或潜伏性感染的进程起关键作用。它们的启动子含有所谓的TAATGARAT基序，这些基序通过一种多蛋白复合物被激活，该复合物包括细胞蛋白Oct-1和HCF以及病毒激活剂（VP16 (= Vmw65, αTIF)）。相对于ICP4启动子的TAATGAGAT序列，ICP0启动子基序有一个5'端延伸，其中包括一个完整的八聚体序列（ATGCTAATGATAT）。似乎这种重叠的八聚体位点可能通过允许Oct-1/VP16复合物更紧密结合或更容易受到其他Oct蛋白的抑制，从而使ICP0启动子元件更具活性。我们的实验支持前一种可能性。一方面，与ICP4位点相比，延伸的ICP0位点显示出Oct-1/VP16复合物更强的结合。此外，带有多个ICP0位点的报告基因的转录在转染细胞中被VP16强烈激活。另一方面，ICP0位点对不同的Oct因子（N-Oct2 = Brn1）的抑制作用基本不敏感，该因子与Oct-1/VP16竞争该位点。与之形成鲜明对比的是，ICP4的传统TAATGAGAT基序的多个拷贝被VP16激活的程度很低，并且该位点的转录可被N-Oct2完全抑制。然而，包含来自ICP4启动子的相邻CGGAAR基序（其结合因子GABPα和β）会导致强烈的协同激活。这种活性，与完整的ICP4启动子的活性一样，对竞争性N-Oct2的抑制作用变得不敏感。因此，ICP4的标准TAATGARAT基序本身比延伸的ICP0基序活性更低且更容易受到抑制，其激活取决于与相邻DNA位点及其同源因子的协同作用。这两种类型的TAATGARAT基序之间的差异可能允许通过因子组合进行更复杂的转录调控。
