Carboxyl-Terminal Region of the Maturation Protein of RNA Coliphage Qβ Mediates Host Attachment, Virion Formation, and Cell Lysis

The single-stranded RNA coliphage Qβ infects Escherichia coli by attaching to the host F-pilus and entering the host cells. The maturation protein (A2) within the virion is thought to mediate these events in the host cell. In this study, we investigated the functional domains of A2 by isolating infectious and noninfectious particles produced in cells harboring Qβ cDNAs with mutations in the distal region of the A2 gene. Noninfectious particles with capsids lacking A2 failed to adsorb to the F-pilus, and A2 protein missing the C-terminal region was not incorporated into the capsid. Several A2 mutants also exhibited reduced cell lysis. These findings demonstrate that the conserved C-terminal region of A2 is involved in several functions, including host binding, complete virion formation, and cell lysis by A2. This study provides a foundation for elucidating the mechanism by which the viral genome enters the host.