Human immunodeficiency virus type 1 integrase stabilizes a linearized HIV-1 LTR plasmid in vivo

A mammalian expression vector designed for production of HIV-1 integrase was found to enhance the stability of a linear reporter plasmid in COS-7 cells. The effect is strictly dependent on coexpression of the HIV-1 rev gene and on the inclusion of U3 and U5 portions of the HIV-1 LTR in the reporter plasmid. Integrase point mutations P109S and D116N drastically reduced stabilization whereas T115A and D64A had little or no effect. Immunoblot analysis revealed the presence of a 32-34kDa integrase protein in extracts of transfected COS-7 cells and of wild type and mutant integrase proteins at comparable levels. We conclude that integrase acts in trans in COS-7 cells, possibly by binding to the HIV-1 LTR in the plasmid. This transfection system may be useful for studying factors that stabilize the HIV-1 DNA genome prior to its integration into the host cell chromosome.