Figure 3

The sequential revolution in translocating dsDNA. (A) The φ29 DNA packaging motor is made of a hexameric ATPase gp16, a hexameric pRNA ring [11] and a dodecameric gp10 connector [12], which form three-coaxial rings [12]. During the viral DNA packaging, ATP shifts one subunit of ATPase gp16 toward a conformation with low entropy but high affinity for dsDNA, which is reversed once the ATP is hydrolyzed, causing a power stroke that pushes the dsDNA toward the adjacent subunit around the diameter of the ATPase tunnel wall. Six ATPs complete a cycle, with one ATP hydrolyzed per step, to achieve one helical turn of 360º (10.5 bp). Rotation of either the DNA or the hexameric ring is unlikely. (B) Diagram of CryoEM results showing the position of dsDNA in the channel wall of bacteriophage T7 DNA packaging motor. (C) The dsDNA revolving along the 12 subunits. (Adopted from reference [24] with the permission from the publisher).