HIV integrase (IN) is a viral enzyme required for integration of virus DNA into the host chromosome. This type of integration is highly specific for retroviruses, and HIV-1 IN is therefore a target for antiviral therapy. To design antivirals, it is essential to characterize IN. We have expressed the IN gene in E. coli as a fusion protein. The cloned IN is reactive with both HIV-1 and HIV-2 positive patient sera in ELISA, while rabbit antisera to the recombinant protein are reactive only with HIV-1 IN but not HIV-2 IN by Western blot. These data have been published in AIDS Res. Hum. Retro. Hybridomas have been prepared using the IN expressing clone and the MAbs are reactive with HIV-1 but not HIV-2 by Western blot. An invention report has been filed and a manuscript is in preparation. Additional clones expressing the N- and C-terminal halves of IN have been constructed and the proteins they express examined for ability to bind DNA using a Southwestern blotting procedure. The complete IN molecule as well as the C-terminal protein bind DNA; the N-terminal portion exhibits no binding activity, suggesting that the C-terminal region contains the DNA binding site. A manuscript has recently been published in AIDS Res. Hum. Retro. We have purified our full-length recombinant IN and it exhibits activity in a specific in vitro assay for enzyme activity involving cleavage of 2 bp from an oligonucleotide corresponding to the HIV-1 LTR. Since our IN is produced as a fusion protein containing 13 amino acids of lambda cII at its amino terminus, detection of activity with our protein indicates that a free amino-terminus is not required for activity. This may be relevant to the in vivo situation, since IN is initially synthesized as a polyprotein linked to RT at its amino-terminus. To more precisely localize the DNA binding site within the C-terminal half of the molecule, we have constructed a series of additional subclones and we are currently purifying the deleted proteins they produce for analysis of DNA binding. We have recently established a collaboration with David Davies at the NIH to provide him with large quantities of IN MAb for generation of Fab fragments for X-ray crystallography of IN, which may eventually facilitate design of enzyme inhibitors.
