Bieniasz P D, Grdina T A, Bogerd H P, Cullen B R
Howard Hughes Medical Institute and Department of Genetics, Duke University Medical Center, Durham, North Carolina 27710, USA.
J Virol. 1999 Jul;73(7):5777-86. doi: 10.1128/JVI.73.7.5777-5786.1999.
The biological activity of the human immunodeficiency virus type 1 (HIV-1) Tat (Tat1) transcriptional activator requires the recruitment of a Tat1-CyclinT1 (CycT1) complex to the TAR RNA target encoded within the viral long terminal repeat (LTR). While other primate immunodeficiency viruses, such as HIV-2 and mandrill simian immunodeficiency virus (SIVmnd), also encode Tat proteins that activate transcription via RNA targets, these proteins differ significantly, both from each other and from Tat1, in terms of their ability to activate transcription directed by LTR promoter elements found in different HIV and SIV isolates. Here, we show that CycT1 also serves as an essential cofactor for HIV-2 Tat (Tat2) and SIVmnd Tat (Tat-M) function. Moreover, the CycT1 complex formed by each Tat protein displays a distinct RNA target specificity that accurately predicts the level of activation observed with a particular LTR. While Tat2 and Tat-M share the ability of Tat1 to bind to CycT1, they differ from Tat1 in that they are also able to bind to the related but distinct CycT2. However, the resultant Tat-CycT2 complexes fail to bind TAR and are therefore abortive. Surprisingly, mutation of a single residue in CycT2 (asparagine 260 to cysteine) rescues the ability of CycT2 to bind Tat1 and also activates not only TAR binding by all three Tat-CycT2 complexes but also Tat function. Therefore, the RNA target specificity of different Tat-CycT1 complexes is modulated by natural sequence variation in both the viral Tat transcriptional activator and in the host cell CycT molecule recruited by Tat. Further, the RNA target specificity of the resultant Tat-CycT1 complex accurately predicts the ability of that complex to activate transcription from a given LTR promoter element.
1型人类免疫缺陷病毒（HIV-1）转录激活因子Tat（Tat1）的生物活性需要将Tat1-细胞周期蛋白T1（CycT1）复合物募集到病毒长末端重复序列（LTR）中编码的TAR RNA靶点上。虽然其他灵长类免疫缺陷病毒，如HIV-2和山魈猴免疫缺陷病毒（SIVmnd），也编码通过RNA靶点激活转录的Tat蛋白，但这些蛋白在激活不同HIV和SIV分离株中发现的LTR启动子元件所指导的转录能力方面，彼此之间以及与Tat1都有显著差异。在这里，我们表明CycT1也是HIV-2 Tat（Tat2）和SIVmnd Tat（Tat-M）功能的必需辅助因子。此外，每种Tat蛋白形成的CycT1复合物表现出独特的RNA靶点特异性，准确预测了特定LTR观察到的激活水平。虽然Tat2和Tat-M具有与Tat1结合CycT1的能力，但它们与Tat1的不同之处在于它们也能够结合相关但不同的CycT2。然而，由此产生的Tat-CycT2复合物无法结合TAR，因此是无效的。令人惊讶的是，CycT2中单个残基的突变（天冬酰胺260突变为半胱氨酸）挽救了CycT2结合Tat1的能力，不仅激活了所有三种Tat-CycT2复合物与TAR的结合，还激活了Tat功能。因此，病毒Tat转录激活因子和Tat募集的宿主细胞CycT分子中的自然序列变异调节了不同Tat-CycT1复合物的RNA靶点特异性。此外，所得Tat-CycT1复合物的RNA靶点特异性准确预测了该复合物从给定LTR启动子元件激活转录的能力。
