Fig. 4.

The ring ATPase is a set of five molecular switches arranged in a closed configuration. (1) The DNA-bound subunit releases ADP on interacting with the DNA (red loop in the subunit; red). (2) The subunits display poor ATPase activity during the ATP-binding phase (light blue). Each subunit uses its arginine finger to facilitate ADP release in its neighbor. All of the subunits bind ATP in a sequential manner. Hydrolysis can only take place slowly at a basal spontaneous rate. (3) The subunit contacting the DNA hydrolyzes ATP first (navy). (4) The subunits display efficient ATPase activities during the translocating phase (orange). Each subunit uses its arginine finger to activate ATP hydrolysis in its neighbor, resulting in a rapid hydrolysis cascade. (Center) Schematic representation of each regulatory mechanism in the context of a molecular packaging trajectory.