An ATP-free packaging of T4 DNA

Abstract

Packaging of viral DNA into a capsid with the liquid crystalline density is a crucial step of the viral reproduction. The DNA packaging with the ATP fueled molecular motor is an established packaging system of viral DNA. However, the velocity and the efficiency are not well match with the 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 ambient concentration of phosphate decreases to the extra-cell concentration in the coexistence with divalent cations, Ca2+ and Mg2+. 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. The conformational changes of DNA between compact forms and coil forms were differentiated by the fluorescent microscopy. Identification between packaged- or unpackaged-DNA was confirmed by enzymatically. The infectious ability of the re-generated virions was confirmed by pfu. The concentration of ATP in the packaging process was measured by 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 conventional and new packaging processes may cooperate to accomplish the DNA packaging process of T4. The results may provide new interpretations of the life cycle of T4.