An ATP-free packaging of T4 DNA

Abstract

Packaging of viral DNA into a capsid with liquid crystalline density is a crucial step in viral reproduction. DNA packaging with an adenosine triphosphate (ATP)-fueled molecular motor is an established viral DNA packaging mechanism system. On the other hand, DNA is compacted by the conformational change attributable to multivalent cations exclusively at valences higher than three. The conformational change of DNA was not considered as a mechanism of DNA packaging of viruses. Here, T4 DNA, ejected from a capsid in the ambient concentration of phosphate corresponding to the intra-cell concentration, is packaged into the capsid when the phosphate concentration decreases to the extra-cell concentration in coexistence with divalent cations, that is, Ca2+ and Mg2+. The compaction and packaging processes coincide with the conformational change of DNA. Divalent cations can compact T4 DNA when the counter anion is phosphate. The DNA-packaged and re-generated virions showed equivalent infective ability with the original populations. Fluorescent microscopy distinguished the conformational changes of DNA between compact forms and coil forms. Packaged or unpackaged DNA was confirmed enzymatically. Plaque-forming unit (Pfu) was used as the measure of infectious ability of virions. The concentration of ATP was measured by the luminometric method. The packaging process was proceeded in picomolar or lower concentration of ATP. This series of procedures may constitute a new ATP-free or low-ATP approach to packaging viral DNA with DNA conformational change underpinning the process. The results from this study may disclose an undiscovered facet of T4 life cycle.