The terminase enzyme from bacteriophage lambda: a DNA-packaging machine

This review focuses on the biochemical, biophysical, and catalytic properti es of terminase, an enzyme involved in bacteriophage lambda genome packagin g. The holoenzyme possesses ATPase, DNA strand-separation, and site-specifi c nuclease activities that work in concert to insert a viral genome into th e confines of a preformed capsid. Moreover, the terminase subunits are part of a series of nucleoprotein complexes involved in genome packaging, inclu ding remarkably stable intermediates that transition to a highly mobile UNA packaging 'machine.' Models for the assembly and interconversion of these complexes are presented. Interactions between the catalytic sites in the en zyme complex, and modulation of these catalytic activities as it relates to the assembly and relative stability of the packaging intermediates are dis cussed. This ordered progression of nucleoprotein intermediates is a common theme in biology as demonstrated by mechanistic similarities between viral DNA packaging, the initiation of chromosomal replication, and the initiati on of transcription. Terminase is thus part of a growing number of examples of biological 'machines' or molecular 'motors.'