Bacteriophage φ29 DNA packaging

Abstract

This chapter discusses the DNA packaging mechanisms of bacteriophage ϕ29. The tailed double-stranded DNA phages share many common features of the packaging process and use a common mechanism. They all package their viral DNA unidirectionally into a preformed capsid precursor called “the prohead.” The DNA substrate for packaging is either a concatemer or a unit-length molecule, depending on the replication strategy of the particular phage. The phages have two packaging proteins, which are responsible for the maturing and the translocation of the DNA. The smaller protein of the pair binds to the DNA while the larger protein interacts with the prohead and binds the smaller subunit to link the prohead and DNA. A prevailing theory of the mechanism is that DNA packaging utilizes the symmetry mismatch between the 5-fold-symmetric icosahedral shell and the 12-fold-symmetric head–tail connector. The ability to transform free energy into motion––a ubiquitous property of biological systems––is manifest dramatically in the translocation of ϕ29 DNA into the prohead. The ϕ29 DNA packaging cascade involves protein, RNA, and DNA conformational changes and movement that are comparable to allosteric regulation in enzyme–substrate interactions.