Overexpression and purification of enzymatically active recombinant integrase protein of Rous sarcoma virus

Removal of nuclease contamination during purification of recombinant prototype foamy virus integrase

Retroviral infection requires integration of the viral genome into the host genome. Recombinant integrase proteins may be purified following bacterial expression. A bulk biochemical assay of integrase function relies on the conversion of supercoiled plasmids to linear or relaxed circles. Single molecule molecular tweezer assays of integrase also evaluate the conversion of supercoiled DNA to nicked and broken species. A bacterial nuclease that co-purifies with retroviral integrase may affect the quantitation of integration activity in bulk or single molecule assays. During purification of retroviral integrase from bacteria, fractions may be screened for contaminating nuclease activity. In order to efficiently separate the nuclease from integrase, the binding affinities of each protein must differ. We find that a co-purifying nuclease may be efficiently separated from integrase based on heparin affinity, but not ionic affinity.

Purification of recombinant Rous sarcoma virus integrase possessing physical and catalytic properties similar to virion-derived integrase

Recombinant Rous sarcoma virus integrase cloned from the Prague A (PrA) virus strain was expressed in Escherichia coli. Here we report the detailed purification procedure resulting in an apparently homogeneous integrase. Recombinant PrA integrase was compared at both the protein structural and the catalytic levels to avian myeloblastosis virus integrase purified from virions. Both proteins exist minimally in a dimeric state at low nanomolar concentrations as analyzed by glycerol gradient sedimentation and protein crosslinking studies. Likewise, both proteins have similar specific activities for full-site (concerted integration reaction) and half-site strand transfer activities using linear 480-bp retrovirus-like donor substrates that contain wild-type or mutant termini. They respond similarly to high NaCl concentrations ( approximately 350 mM) as well as aprotic solvents for efficient full-site strand transfer. The data suggest that recombinant integrase proteins with physical and catalytic properties similar to the virion counterpart can be purified using these techniques and will faithfully and efficiently promote the full-site integration reaction in vitro.