Bacteriophage T4 genome packaging: mechanism and application

It has been a 45-year journey studying genome packaging of a single virus, the tailed bacteriophage T4. T4, then and now, remains a powerful model for understanding viruses, particularly tailed phages, the most abundant and widely distributed organisms on Earth. The biochemistry, structure, and single-molecule dynamics of the T4 DNA packaging motor have been teased out. Packaging ~171 kb genomic DNA into a 120 × 86 nm prolate icosahedral head in a few minutes, the T4 packaging motor is the fastest and most powerful motor known. It is also the most promiscuous, allowing packaging of any double-stranded DNA regardless of sequence or length into various head (capsid) assemblies: unexpanded prohead, expanded prohead, or mature head. These studies established the basic architecture of an ATP-powered viral genome packaging machine consisting of a pentameric packaging motor attached to the dodecameric portal vertex of the capsid shell. Furthermore, it opened new avenues to engineer and repurpose the packaging machine for the delivery of genes, proteins, and protein-nucleic acid complexes into human cells. The biggest challenge now is to translate this knowledge into the design of future phage-vectored gene therapy platforms that allow engineered phages to interact with human cells and make appropriate genetic and metabolic corrections to alleviate disease. This possibility was unimaginable when we started but evolved through lessons learned by examining the intricate machinery of the phage T4 life cycle.