We report key mechanistic differences between the reverse transcriptases (RT) of human immunodeficiency virus type-1 (HIV-1) and of xenotropic murine leukemia virus-related virus (XMRV), a gammaretrovirus that can infect human cells. Steady and pre-steady state kinetics demonstrated that XMRV RT is significantly less efficient in DNA synthesis and in unblocking chain-terminated primers. Surface plasmon resonance experiments showed that the gammaretroviral enzyme has a remarkably higher dissociation rate (koff) from DNA, which also results in lower processivity than HIV-1 RT. Transient kinetics of mismatch incorporation revealed that XMRV RT has higher fidelity than HIV-1 RT. We identified RNA aptamers that potently inhibit XMRV, but not HIV-1 RT. XMRV RT is highly susceptible to some nucleoside RT inhibitors, including Translocation Deficient RT inhibitors, but not to non-nucleoside RT inhibitors. We demonstrated that XMRV RT mutants K103R and Q190M, which are equivalent to HIV-1 mutants that are resistant to tenofovir (K65R) and AZT (Q151M), are also resistant to the respective drugs, suggesting that XMRV can acquire resistance to these compounds through the decreased incorporation mechanism reported in HIV-1.
Bibliographical noteFunding Information:
NIH grants (AI076119, AI079801, and AI094715, to S.G.S.), (AI074389, to D.H.B.), (AI079801 to M.A.P.); NIH Bench-to-Bedside Award and the Intramural Research Program of the NIH, National Cancer Institute, Center for Cancer Research (to V.K.P); Ministry of Knowledge and Economy, Bilateral International Collaborative R&D Program, Republic of Korea; Canadian Institutes of Health Research (CIHR) and University of Missouri (to S-L.L.); amfAR Mathilde Krim Fellowship and a CIHR Fellowship (to B.M.). Funding for open access charge: NIH grants (AI076119, AI094715, AI074389, AI079801).