HIV-2, a human pathogen that causes acquired immunodeficiency syndrome, is distinct from the more prevalent HIV-1 in several features including its evolutionary history and certain aspects of viral replication. Like other retroviruses, HIV-2 packages two copies of full-length viral RNA during virus assembly and efficient genome encapsidation is mediated by the viral protein Gag. We sought to define cis-acting elements in the HIV-2 genome that are important for the encapsidation of full-length RNA into viral particles. Based on previous studies of murine leukemia virus and HIV-1, we hypothesized that unpaired guanosines in the 5′ untranslated region (UTR) play an important role in Gag:RNA interactions leading to genome packaging. To test our hypothesis, we targeted 18 guanosines located in 9 sites within the HIV-2 5′ UTR and performed substitution analyses. We found that mutating as few as three guanosines significantly reduce RNA packaging efficiency. However, not all guanosines examined have the same effect; instead, a hierarchical order exists wherein a primary site, a secondary site, and three tertiary sites are identified. Additionally, there are functional overlaps in these sites and mutations of more than one site can act synergistically to cause genome packaging defects. These studies demonstrate the importance of specific guanosines in HIV-2 5′UTR in mediating genome packaging. Our results also demonstrate an interchangeable and hierarchical nature of guanosine-containing sites, which was not previously established, thereby revealing key insights into the replication mechanisms of HIV-2.

HIV-2 是一种导致获得性免疫缺陷综合征的人类病原体，在包括其进化历史和病毒复制的某些方面在内的几个特征上与更普遍的 HIV-1 不同。与其他逆转录病毒一样，HIV-2 在病毒组装过程中包装了两个全长病毒 RNA 拷贝，并且有效的基因组外壳化由病毒蛋白 Gag 介导。我们试图定义顺式-HIV-2 基因组中的作用元件，这些元件对于将全长 RNA 包裹到病毒颗粒中很重要。基于先前对鼠白血病病毒和 HIV-1 的研究，我们假设 5' 非翻译区 (UTR) 中的未配对鸟苷在 Gag:RNA 相互作用中发挥重要作用，从而导致基因组包装。为了检验我们的假设，我们针对位于 HIV-2 5' UTR 内 9 个位点的 18 个鸟苷进行了替代分析。我们发现突变少至三个鸟苷会显着降低 RNA 包装效率。然而，并非所有检查的鸟苷都具有相同的效果。相反，存在一个分层顺序，其中标识了一个主站点、一个辅助站点和三个第三站点。此外，这些位点存在功能重叠，并且多个位点的突变可以协同作用导致基因组包装缺陷。这些研究证明了 HIV-2 5'UTR 中特定鸟苷在介导基因组包装中的重要性。我们的结果还证明了含鸟苷位点的可互换和分层性质，这是以前未建立的，从而揭示了对 HIV-2 复制机制的关键见解。