During replication, the lengthy genome of dsDNA viruses is translocated with remarkable velocity into a limited space within the protein shell and packaged to crystalline density. This otherwise energetically unfavorable motion task is accomplished by a viral nano-motor. The bacterial virus phi29 DNA-packaging motor uses a mechanism similar to the driving of a bolt with a hex nut1 in that six pRNAs form a hexagonal complex to gear the DNA translocating machine2-4. Sequential action of six RNA molecules to drive the motor1 is similar to the consecutive firing of six cylinders of a car engine.
A particle containing a 40-nm viral DNA-packaging motor has been constructed with purified recombinant proteins and artificially synthesized RNA molecules5,6. ATP is used as a source of enrgy5 for rotation3,6-8. The motor can be turned on with the addition of magnesium and turned off with the addition of EDTA9. This motor has been tested to be the strongest existing nano motor with the highest stalling force of 67 pico-newtons10-12.
The pRNA contains two functional domains: one for DNA translocation and the other for the binding of the twelve-fold symmetrical connector10 that is embedded in a five-fold symmetrical structure1,13. Rotation of the hexameric pRNA within a five-fold/six-fold symmetrical mismatch environment could ensure a continuous rotation of a mechanical motor in which the relative motion of the two rings could produce a driving force to translocate the DNA into the procapsid.