CRYSTALLIZATION OF THE FELINE IMMUNODEFICIENCY VIRUS INTEGRASE PROTEIN. Ann E. Maris¹, Yoshio Shibagaki², Mary L. Kopka³, Thang Kien Chiu¹, Samson A. Chow² and Richard E. Dickerson³, ¹Department of Chemistry and Biochemistry, ²Department of Molecular and Medical Pharmacology^{, 3}Molecular Biology Institute, University of California at Los Angeles, CA 90095

Integrase catalyzes integration of the cDNA copy of the viral genome into the host chromosome, a necessary step in the retroviral life cycle. Integrase processes the U5 and U3 termini of the viral DNA by cleaving off two terminal nucleotides, and leaving a recessed 3'-hydroxyl on both ends. These ends then function as the nucleophiles in a one-step transesterification reaction which leaves the viral DNA covalently joined to the host DNA.

The integrase proteins of human and feline immunodeficiency viruses (HIV and FIV) share about 86% similarity and 37% identity and have similar biochemical activities and sub-domain organization. Three domains have been identified in integrase: the core, containing catalytic activity, the N- and the C-terminus. Only the core's structure has been determined for both HIV and Rous Sarcoma Virus. The N-terminus is necessary for the joining reaction and contains a novel putative zinc-finger, which may be involved in the formation of a stable complex between integrase and viral DNA. We have purified and concentrated to 10 mg/ml a truncated FIV integrase consisting of the N-terminus and the core. Conditions were found to obtain microcrystals consistently and we are further modifying conditions to increase crystal size. In addition, we are exploring various DNA substrates to obtain integrase-DNA co-crystallization.