Single-stranded RNA bacteriophages (ssRNA phages) are small spherical RNA viruses that infect bacteria with retractile pili. The single positive-sense genomic RNA of ssRNA phages, which is protected by a capsid shell, is delivered into the host via the retraction of the host pili. Structures involved in ssRNA phage infection cycle are essential for understanding the underlying mechanisms that can be used to engineer them for therapeutic applications. This review summarizes the recent breakthroughs in high-resolution structural studies of two ssRNA phages, MS2 and Qβ, and their interaction with the host, E. coli, by cryo-electron microscopy (cryo-EM). These studies revealed new cryo-EM structures, which provide insights into how MS2 and Qβ package the RNA, lyse E. coli, and adsorb to the receptor F-pili, responsible for conjugation. Methodologies described here can be expanded to study other ssRNA phages that target pathogenic bacteria.

单链 RNA 噬菌体 (ssRNA 噬菌体) 是小球形 RNA 病毒，可通过可伸缩菌毛感染细菌。由衣壳保护的 ssRNA 噬菌体的单个正义基因组 RNA 通过宿主菌毛的缩回传递到宿主中。ssRNA 噬菌体感染周期中涉及的结构对于理解可用于设计它们以用于治疗应用的潜在机制至关重要。本综述总结了两种 ssRNA 噬菌体 MS2 和 Qβ 的高分辨率结构研究的最新突破，以及它们通过冷冻电子显微镜 (cryo-EM)与宿主大肠杆菌的相互作用。这些研究揭示了新的冷冻电镜结构，从而深入了解 MS2 和 Qβ 如何包装 RNA、裂解大肠杆菌，并吸附到负责结合的受体 F-菌毛上。这里描述的方法可以扩展到研究其他针对病原菌的 ssRNA 噬菌体。