DNA Packaging in Double-Stranded DNA Phages

Abstract

Abstract Imagine trying to stuff a string more than 6mm long into a sphere that is fifty nanometers in diameter. The hole in the sphere that the string must enter is only twice as wide as the string itself. The string is stiff, with a persistence length on the order of 50 nm. It is also negatively charged and self-repulsive. The string must be organized such that it can be pulled out easily, so no knots or tangles are permitted. When the sphere is full, the string will have a near crystalline density. You have several minutes to complete this task. This difficult feat is the challenge presented to dsDNA phages during DNA packaging, a pivotal event in the assembly cascade. The task of compacting the double-stranded DNA chromosome into a protein capsid is a dramatic endeavor. DNA by its nature does not want to be in condensed form, but rather is dispersed, occupying a volume more than 100 times its volume inside the virion (47, 54). Therefore, in order to be packaged, energy must be invested in the DNA. The DNA packaging event must also be coordinated with the replication of the phage DNA that is to be packaged, as well as the assembly and maturation of the protein capsid. Numerous investigators, using a battery of model phage systems, have made a concerted effort over four decades to resolve the components and mechanism of DNA packaging.