Bacteriophage T7 DNA Translocation during Infection is Bolstered by the Host ATP Synthase Complex

Abstract

Translocation of bacteriophage T7 dsDNA into its host cell is an integral step in infection initiation that is energy dependent and is catalyzed principally by transcription per host and viral RNA polymerases. Here we show utilizing high-throughput cryo-electron tomography, a hexameric ring complex exists below the T7 trans-envelope channel in the host-cell cytoplasm during infection. Using sub-tomogram averaging and extensive classification we isolated T7 in the brief stage of genome translocation in coordination with the ring. This host-cell nanomachine is ∼30nm in diameter, ∼8nm in height with a ∼10nm channel. The complex was not observed in ATP synthase-deficient Escherichia coli mutants, suggesting that the complex functions in an energy-dependent manner. T7 grows in these mutant strains, and thus DNA ejection is not dependent on the complex. The ring is not host-specific; it has also been observed in an infected rough strain of Salmonella typhimurium, which supports the growth of T7. These results, only obtainable by in situ structural analysis, provide details on the essential process of DNA translocation and reveal the ability of T7 to recruit host-cell machinery to aid in the initiation of infection.