The dsDNA packaging motor in bacteriophage ø29

The tailed dsDNA bacteriophage ø29 packages its 19.3-kb genome into a preassembled prolate icosahedral procapsid structure using a phage-encoded macromolecular motor. This process is remarkable considering that compaction of DNA to near crystalline densities within the confined space of the capsid requires that the motor work against considerable entropic, enthalpic, and DNA bending energies. The heart of the bacteriophage ø29 packaging motor consists of three macromolecular components: the connector protein, an RNA molecule known as the pRNA, and an ATPase. The pRNA is thus far unique to ø29, but the connector and ATPase are homologous to portal and terminase proteins, respectively, in other tailed dsDNA bacteriophages. Despite decades of effort and a wealth of genetic, biochemical, biophysical, structural, and single particle data, the mechanism of DNA packaging in bacteriophage ø29 remains elusive. In this chapter, we describe the development of a highly efficient in vitro DNA packaging system for ø29, review the data available for each individual macromolecular component in the packaging motor, and present and evaluate various packaging mechanisms that have been proposed to explain the available data.