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Intrinsic DNA synthesis fidelity of xenotropic murine leukemia virus-related virus reverse transcriptase
Vernica Barrioluengo1, Yi Wang2, Stuart F. J. Le Grice2, Luis Menndez-Arias1,*
Although recent reports have provided strong evidence to suggest that xenotropic murine leukemia virus-related virus (XMRV) is unlikely to be the causative agent of prostate cancer and chronic fatigue syndrome, this recombinant retrovirus can nonetheless infect human cells in vitro and induce a chronic infection in macaques. We have determined the accuracy of DNA synthesis of the reverse transcriptases (RTs) of XMRV and Moloney murine leukemia virus (MoMLV) using a combination of pre-steady-state kinetics of nucleotide incorporation and an M13mp2-based forward mutation assay. The obtained results have been compared with those previously reported for the human immunodeficiency virus type 1 BH10 strain (HIV-1BH10) RT. MoMLV and XMRV RTs were 13.9 and 110 times less efficient (as determined by kpol/Kd) than the HIV-1BH10 RT in incorporating correct nucleotides. Misinsertion and mispair extension kinetic studies demonstrated that MoMLV RT was more accurate than the HIV-1BH10 RT. In comparison with MoMLV RT, the XMRV enzyme showed decreased mispair extension fidelity and was less faithful when misincorporating C or A opposite A. However, the XMRV RT showed stronger selectivity against G in misinsertion fidelity assays. Forward mutation assays revealed that XMRV and MoMLV RTs had similar accuracy of DNA-dependent DNA synthesis, but were >13 times more faithful than the HIV-1BH10 enzyme. The mutational spectra of XMRV and MoMLV RTs were similar in having a relatively higher proportion of frameshifts and transversions, compared with the HIV-1BH10 RT. However, the XMRV polymerase was less prone to introduce large deletions and one-nucleotide insertions.