DNA Repair Enzyme Uracil DNA Glycosylase Is Specifically Incorporated into Human Immunodeficiency Virus Type 1 Viral Particles through a Vpr-Independent Mechanism

The Vpr protein, encoded by the human immunodeficiency virus type 1 (HIV-1) genome, is one of the nonstructural proteins packaged in large amounts into viral particles. We have previously reported that Vpr associates with the DNA repair enzyme uracil DNA glycosylase (UDG). In this study, we extended these observations by investigating whether UDG is incorporated into virions and whether this incorporation requires the presence of Vpr. Our results, with highly purified viruses, show that UDG is efficiently incorporated either into wild-type virions or into Vpr-deficient HIV-1 virions, indicating that Vpr is not involved in UDG packaging. Using an in vitro protein-protein binding assay, we reveal a direct interaction between the precursor form of UDG and the viral integrase (IN). Finally, we demonstrate that IN-defective viruses fail to incorporate UDG, indicating that IN is required for packaging of UDG into virions.

人类免疫缺陷病毒1型（HIV-1）基因组编码的Vpr蛋白，是可被大量包装进入病毒颗粒的非结构蛋白之一。我们此前曾报道，Vpr可与DNA修复酶尿嘧啶DNA糖苷酶（UDG）相结合。本研究中，我们针对前述研究发现展开了拓展性探究：即UDG是否会被包装进入病毒颗粒，以及该包装过程是否需要Vpr的参与。针对高度纯化病毒的实验结果显示，UDG可高效地被包装进入野生型HIV-1病毒颗粒，或是Vpr缺陷型HIV-1病毒颗粒，这表明Vpr并未参与UDG的病毒颗粒包装过程。通过体外蛋白质-蛋白质结合实验，我们发现UDG的前体形式可与病毒整合酶（IN）发生直接相互作用。最后，我们证实整合酶缺陷型病毒无法完成UDG的包装，这表明UDG的病毒颗粒包装过程依赖于整合酶的存在。