Alternative divalent cations (Zn2+, Co2+, and Mn2+) are not mutagenic at conditions optimal for HIV-1 reverse transcriptase activity

Background: Fidelity of DNA polymerases can be influenced by cation co-factors. Physiologically, Mg2+ is used as a co-factor by HIV reverse transcriptase (RT) to perform catalysis; however, alternative cations including Mn2+, Co2+, and Zn2+ can also support catalysis. Although Zn2+ supports DNA synthesis, it inhibits HIV RT by significantly modifying RT catalysis. Zn2+ is currently being investigated as a component of novel treatment options against HIV and we wanted to investigate the fidelity of RT with Zn2+. Methods: We used PCR-based and plasmid-based alpha complementation assays as well as steady-state misinsertion and misincorporation assays to examine the fidelity of RT with Mn2+, Co2+, and Zn2+. Results: The fidelity of DNA synthesis by HIV-1 RT was approximately 2.5 fold greater in Zn2+ when compared to Mg2+ at cation conditions optimized for nucleotide catalysis. Consistent with this, RT extended primers with mismatched 3' nucleotides poorly and inserted incorrect nucleotides less efficiently using Zn2+ than Mg2+. In agreement with previous literature, we observed that Mn2+ and Co2+ dramatically decreased the fidelity of RT at highly elevated concentrations (6 mM). However, surprisingly, the fidelity of HIV RT with Mn2+ and Co2+ remained similar to Mg2+ at lower concentrations that are optimal for catalysis. Conclusion: This study shows that Zn2+, at optimal extension conditions, increases the fidelity of HIV-1 RT and challenges the notion that alternative cations capable of supporting polymerase catalysis are inherently mutagenic.