Integration host factor: A protein for all reasons

The identification and characterization of the Escherichia coli DNA binding protein integration host factor (IHF) is an elegant example of how a well-characterized virus can be employed in the analysis of a host function. In this case, Nash and coworkers, through their landmark in vitro studies of coliphage lambda site-specific recombination, have identified a protein that plays roles not only in other recombination reactions, but also in DNA replication and regulation of gene expression. IHF belongs to a class of structurally related "histonelike" proteins that can wrap DNA into higher-order structures. The most abundant of these proteins in E. coli is HU, and others have been found in a number of bacterial genera as well as archaebacteria. In addition to site-specific recombination, other aspects of lambda development influenced by IHF have been fertile sources of information about this protein. The author initially focuses on studies with lambda that serve to present the basic information about IHF and then examine the various roles for IHF derived from studies of E. coli and some of its other phages and plasmids.