The role of himA and xis in lambda site-specific recombination

Abstract

We have examined the requirements for integrative and excisive recombination of bacteriophage γ, by providing large quantities of Int and varying amounts of Xis in him A + and him A mutant cells. The wild type him A gene product is not essential for excisive recombination in the presence of large amounts of Xis. When Xis is limiting or missing, however, the him A gene product plays a major role in excision. Similarly, integrative recombination is normally quite dependent on him A product. Limited integrative recombination can occur in a him A mutant, but only in the presence of large quantities of Xis. We propose that alternative pathways exist for these two reactions; one pathway (int, Him A) is favored for integration but can be used for excision, while the other (Int, Xis) is highly efficient for excisive recombination but can also be used for integrative recombination.