Purification of Single-Stranded RNA Bacteriophages and Host Receptors for Structural Determination Using Cryo-Electron Microscopy

Single-stranded RNA bacteriophages (ssRNA phages) are small viruses with a compact genome (~3–4 kb) that infect gram-negative bacteria via retractile pili. These phages have been applied in various fields since their discovery approximately 60 years ago. To understand their biology, it is crucial to analyze the structure of mature virions. Cryo-electron microscopy (cryo-EM) has been employed to determine the structures of two ssRNA phages, MS2 and Qβ. This chapter presents a method for purifying these two phages and their receptor, the F-pilus, to allow examination using cryo-EM.