Purification and characterization of HIV-1 reverse transcriptase having a 1:1 ratio of p66 and p51 subunits

Wild-type and several mutant forms of recombinant human immunodeficiency virus type-1 reverse transcriptase were overexpressed as either the p66 or the p51 subunit in a protease-deficient strain of Escherichia coli. Immediately prior to cell lysis, p51 cell paste was mixed with cell paste containing the corresponding overexpressed p66 subunit in a ratio resulting in an excess of the smaller subunit with respect to the larger. During the subsequent chromatography steps stable heterodimer p66/p51 was purified to homogeneity. This protein was characterized by amino acid analysis, denaturing sodium dodecyl sulfate-polyacrylamide gel electrophoresis, analytical gel filtration HPLC, laser desorption mass spectroscopy, and isoelectric focusing. In addition, we were able to obtain crystals of the purified enzyme complexed with a quinazolinone class nonnucleoside inhibitor that diffracted to 3.2 A resolution. A potential application of this expression/purification methodology is the ability to alter specific amino acids residues, by site-directed-mutagenesis, of only one subunit of the RT-dimer.