An ATP-free packaging of T4 DNA

Abstract Packaging of viral DNA into a capsid with the liquid crystalline density is a crucial step in viral reproduction. The DNA packaging with the ATP fueled molecular motor is an established viral DNA packaging system. However, the velocity and the efficiency are not well matched with in vivo processes. On the other hand, DNA compacts with the conformational change by multivalent cations exclusively of the valences higher than three. The conformational change of DNA was not considered as the vehicle 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 the coexistence with divalent cations, Ca 2+ and Mg 2+ . The compaction and packaging process 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 were confirmed enzymatically. Pfu was used as the measure of infectious ability of virions. The concentration of ATP was measured by the luminometric method. The packaging is proceeded in pM or lower concentration of ATP. This is a new packaging process of viral DNA practically free from ATP into which conformational change of DNA is incorporated. The results may provide new interpretations of the life cycle of T4.