Essentially all organisms harbor enzymes (proteins) that are able to move discrete segments of DNA from one genomic location to another. Their presence provides a way for organisms to respond to environmental changes, and they have been shown to be major drivers of genome evolution. Interestingly, one of these protein systems appears to have been used by higher organisms to shuffle pieces of DNA in order to generate antibodies. We would like to understand how these proteins work. Our main approach has been to use a method of determining 3-dimensional structure, known as x-ray crystallography, as a way to visualize these proteins as they interact with DNA.