We have used the yeast two-hybrid system to study various protein-protein interactions important in retrovirus replication. Homodimerization of HIV-1 Gag and Integrase (IN) proteins is readily detected. The minimal regions required for binding have been defined genetically, and interaction-negative point mutants have been recovered from appropriate screens. Most importantly, the system can be used to identify host cellular proteins that bind to viral proteins. By screening large libraries, the HIV-1 Gag protein was found to bind specifically to cyclophilin A (CypA), a ubiquitously-expressed enzyme required for proper protein folding. CypA is an abundant protein in the HIV-1 virion particle. The Gag-CypA interaction, disrupted by the cyclosporin drugs is essential for virus replication. Other experiments have led to the identification of at least two novel genes whose proteins bind tightly to all retroviral Gag proteins. Similarly, a single host protein, dubbed hSnf5 or Ini-1, was found to interact with the HIV-1 integrase. Ini-1 stimulates IN function in vitro, and may serve to target incoming viral DNA to selected regions of the host genome. These studies provide new assays for antiviral drugs, and serve to identify new potential points for intervention.

Amino Acid Isomerases/METABOLISM Carrier Proteins/METABOLISM DNA Nucleotidyltransferases/METABOLISM DNA, Viral/METABOLISM DNA-Binding Proteins/GENETICS/METABOLISM Gene Products, gag/METABOLISM HIV-1/ENZYMOLOGY/METABOLISM/PHYSIOLOGY Point Mutation Protein Binding Proteins/GENETICS/*METABOLISM Viral Proteins/*METABOLISM Virus Replication ABSTRACT

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