Single-molecule studies of viral DNA packaging

Assembly of many dsDNA viruses involves packaging of DNA molecules into pre-assembled procapsids by portal molecular motor complexes. Techniques have recently been developed using optical tweezers to directly measure the packaging of single DNA molecules into single procapsids in real time and the forces generated by the molecular motor. Three different viruses, phages phi29, lambda, and T4, have been studied, revealing interesting similarities and differences in packaging dynamics. Single-molecule fluorescence methods have also been used to measure packaging kinetics and motor conformations. Here we review recent discoveries made using these new techniques.

► Single viral DNA packaging events can be measured in real time with optical tweezers.
► Viral packaging motors are among the strongest and fastest known molecular motors.
► High electrostatic repulsion forces resist packaging and can trigger capsid expansion.
► Single-molecule fluorescence can measure packaging kinetics/conformational changes.
► Effects of alterations in motor and DNA structure reveal aspects of motor mechanisms.