PHOTO-CROSS-LINKING STUDIES SUGGEST A MODEL FOR THE ARCHITECTURE OF AN ACTIVE HUMAN-IMMUNODEFICIENCY-VIRUS TYPE-1 INTEGRASE-DNA COMPLEX

The virally encoded integrase protein carries out retroviral integrati on, which requires specific interactions with the two ends of the vira l DNA, and also with host DNA that is the target of integration. We at tached a photo-cross-linking agent to specific viral and target DNA si tes to identify regions of the integrase polypeptide that are in close proximity to those substrate features in the active integrase-DNA com plex. The active form of integrase is a multimer. The higher-order org anization of the active integration complex was therefore investigated by determining whether specific cross-links occurred to the active-si te containing protomer. Both viral and target DNA cross-links to human immunodeficiency virus type 1 (HIV-1) integrase mapped predominantly to integrase protomers in trans to the active site, in a multimeric in tegrase complex. The results provide the basis for a model of the prot ein-DNA architecture of an active HIV-1 integration complex that sugge sts specific functions for the N-terminal, core, and C-terminal domain s of retroviral integrase. One implication of this model is that the i ntegrase multimer that mediates concerted integration of the viral DNA ends is composed of at least eight integrase protomers.