The present invention provides methods of identifying agents that reduce a level of active APOBEC3C in a cell. The present invention provides agents that reduce a level of active APOBEC3C in a cell and compositions comprising the agents. The present invention further provides methods of reducing the mutation rate of a lentivirus in a cell and methods of reducing the emergence of drug-resistant strains of lentivirus. The present invention further provides methods for treating lentivirus infections.