Human T cell leukemia virus type 1 (HTLV-1) immature particles differ in morphology from other retroviruses, suggesting a distinct way of assembly. Here we report the results of cryo-electron tomography studies of HTLV-1 virus-like particles assembled in vitro, as well as derived from cells. This work shows that HTLV-1 uses a distinct mechanism of Gag–Gag interactions to form the immature viral lattice. Analysis of high-resolution structural information from immature capsid (CA) tubular arrays reveals that the primary stabilizing component in HTLV-1 is the N-terminal domain of CA. Mutagenesis analysis supports this observation. This distinguishes HTLV-1 from other retroviruses, in which the stabilization is provided primarily by the C-terminal domain of CA. These results provide structural details of the quaternary arrangement of Gag for an immature deltaretrovirus and this helps explain why HTLV-1 particles are morphologically distinct.

人类 T 细胞白血病病毒 1 型 (HTLV-1) 未成熟颗粒的形态与其他逆转录病毒不同，表明其组装方式不同。在这里，我们报告了体外组装以及细胞衍生的 HTLV-1 病毒样颗粒的冷冻电子断层扫描研究结果。这项工作表明，HTLV-1 使用独特的 Gag-Gag 相互作用机制来形成未成熟的病毒晶格。对未成熟衣壳 (CA) 管状阵列的高分辨率结构信息的分析表明，HTLV-1 的主要稳定成分是 CA 的 N 端结构域。诱变分析支持了这一观察结果。这将 HTLV-1 与其他逆转录病毒区分开来，后者的稳定性主要由 CA 的 C 端结构域提供。这些结果提供了未成熟δ逆转录病毒的 Gag 四级排列的结构细节，这有助于解释为什么 HTLV-1 颗粒在形态上不同。