This application proposes to study the process of HIV integration by (1) purifying preintegrative complexes to near homogeneity and determine the protein composition and stoichiometry, (2) characterizing the structure of isolated preintegrative complexes in detail using electron microscopy and assays for protein-DNA interactions, and (3) to build upon the exciting finding that HMG I(Y) is a likely component of the preintegrative complex by examining its role in the integration process in vivo and in vitro.