During HIV-1 assembly, the viral Gag polyprotein specifically selects the dimeric RNA genome for packaging into new virions. The 5′ untranslated region (5′UTR) of the dimeric genome may adopt a conformation that is optimal for recognition by Gag. Further conformational rearrangement of the 5′UTR, promoted by the nucleocapsid (NC) domain of Gag, is predicted during virus maturation. Two 5′UTR dimer conformations, the kissing dimer (KD) and the extended dimer (ED), have been identified in vitro, which differ in the extent of intermolecular basepairing. Whether 5′UTRs from different HIV-1 strains with distinct sequences have access to the same dimer conformations has not been determined. Here, we applied fluorescence cross-correlation spectroscopy and single-molecule Förster resonance energy transfer imaging to demonstrate that 5′UTRs from two different HIV-1 subtypes form (KDs) with divergent stabilities. We further show that both 5′UTRs convert to a stable dimer in the presence of the viral NC protein, adopting a conformation consistent with extensive intermolecular contacts. These results support a unified model in which the genomes of diverse HIV-1 strains adopt an ED conformation.

在 HIV-1 组装过程中，病毒 Gag 多蛋白专门选择二聚体 RNA 基因组来包装成新的病毒颗粒。二聚体基因组的 5' 非翻译区 (5'UTR) 可能采用最适合 Gag 识别的构象。在病毒成熟过程中，预计由 Gag 的核衣壳 (NC) 结构域促进 5'UTR 的进一步构象重排。两种 5'UTR 二聚体构象，接吻二聚体 (KD) 和延伸二聚体 (ED)，已在体外鉴定，它们在分子间碱基配对的程度上不同。来自具有不同序列的不同 HIV-1 毒株的 5'UTR 是否具有相同的二聚体构象尚未确定。这里，我们应用荧光互相关光谱和单分子 Förster 共振能量转移成像来证明来自两种不同 HIV-1 亚型的 5'UTR 形成具有不同稳定性的 (KD)。我们进一步表明，在病毒 NC 蛋白存在的情况下，两个 5'UTR 都转化为稳定的二聚体，采用与广泛的分子间接触一致的构象。这些结果支持一个统一模型，其中不同 HIV-1 毒株的基因组采用 ED 构象。