Protein and DNA requirements of the bacteriophage HP1 recombination system: a model for intasome formation.

A fundamental step in site-specific recombination reactions involves the formation of properly arranged protein-DNA structures termed intasomes. The contributions of various proteins and DNA binding sites in the intasome determine not only whether recombination can occur, but also in which direction the reaction is likely to proceed and how fast the reaction will go. By mutating individual DNA binding sites and observing the effects of various mixtures of recombination proteins on the mutated substrates, we have begun to categorize the requirements for intasome formation in the site-specific recombination system of bacteriophage HP1. These experiments define the binding site occupancies in both integrative and excessive recombination for the three recombination proteins: HP1 integrase, HP1 Cox and IHF. This data has allowed us to create a model which explains many of the biochemical features of HP1 recombination, demonstrates the importance of intasome components on the directionality of the reaction and predicts further ways in which the role of the intasome can be explored.