Transposition is a genetic rearrangement process in which DNA sequences termed transposable elements "move" from one DNA location to another. Transposable elements can also cause deletions, inversions and chromosome fusions. A molecular understanding of the transposition process is important because: similar DNA rearrangements are likely to have played an important role in genome evolution and in the somatic cell chromosome changes associated with some cancers, retroviruses such as HIV-I integrate into host chromosomes through a transposition like process, and bacterial transposable elements frequently carry (and help disseminate) antibiotic resistance genes. Furthermore, transposable elements raise fundamental biochemical questions that are important to address, such as: how do proteins "recognize" specific DNA sequences what is the molecular basis for cis activity by some DNA metabolizing proteins, how can a protein (and a DNA sequence) be configured to perform multiple sequential reactions. We are planning to use the bacterial Tn5/IS50 transposon system to study the molecular basis for transposition. The studies will use detailed genetic, biochemical and crosslinking strategies to study the molecular details of how the IS50/Tn5 transposase and end DNA sequences function during transposition. The following transposition reactions will be studied: the transposase-end sequence binding reaction, the DNA cleavage reaction, and the DNA strand transfer reaction. We will also study the molecular basis for transposase cis activity; believed to be related to the transposase-transposase oligomerization reaction.