| Summary: | <p>Abstract</p> <p>Background</p> <p>HIV-1 subtype C infections account for over half of global HIV infections, yet the vast focus of HIV-1 research has been on subtype B viruses which represent less than 12% of the global pandemic. Since HIV-1 reverse transcriptase (RT) is a major target of antiviral therapy, and since differential drug resistance pathways have been observed among different HIV subtypes, it is important to study and compare the enzymatic activities of HIV-1 RT derived from each of subtypes B and C as well as to determine the susceptibilities of these enzymes to various RT inhibitors in biochemical assays.</p> <p>Methods</p> <p>Recombinant subtype B and C HIV-1 RTs in heterodimeric form were purified from <it>Escherichia coli </it>and enzyme activities were compared in cell-free assays. The efficiency of (-) ssDNA synthesis was measured using gel-based assays with HIV-1 PBS RNA template and tRNA<sub>3</sub><sup>Lys </sup>as primer. Processivity was assayed under single-cycle conditions using both homopolymeric and heteropolymeric RNA templates. Intrinsic RNase H activity was compared using 5'-end labeled RNA template annealed to 3'-end recessed DNA primer in a time course study in the presence and absence of a heparin trap. A mis-incorporation assay was used to assess the fidelity of the two RT enzymes. Drug susceptibility assays were performed both in cell-free assays using recombinant enzymes and in cell culture phenotyping assays.</p> <p>Results</p> <p>The comparative biochemical analyses of recombinant subtype B and subtype C HIV-1 reverse transcriptase indicate that the two enzymes are very similar biochemically in efficiency of tRNA-primed (-) ssDNA synthesis, processivity, fidelity and RNase H activity, and that both enzymes show similar susceptibilities to commonly used NRTIs and NNRTIs. Cell culture phenotyping assays confirmed these results.</p> <p>Conclusions</p> <p>Overall enzyme activity and drug susceptibility of HIV-1 subtype C RT are comparable to those of subtype B RT. The use of RT inhibitors (RTIs) against these two HIV-1 enzymes should have comparable effects.</p>
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