Effect of 8-Oxo-1,N⁶-Ethenoadenine Derivatives on the Activity of RNA Polymerases from SARS-CoV-2 and Escherichia coli

Bacterial and viral RNA polymerases are promising targets for the development of new transcription inhibitors. One of the potential blockers of RNA synthesis is 7,8-dihydro-8-oxo-1,N⁶-ethenoadenine (oxo-εA), a synthetic compound that combines two adenine modifications: 8-oxoadenine and 1,N⁶-ethenoadenine. In this study, we synthesized oxo-εA triphosphate (oxo-εATP) and showed that it could be incorporated by the RNA-dependent RNA polymerase of SARS-CoV-2 into synthesized RNA opposite template residues A and G in the presence of Mn²⁺ ions. Escherichia coli RNA polymerase incorporated oxo-εATP opposite A residues in the template DNA strand. The presence of oxo-εA instead of adenine in the template DNA strand completely stopped transcription at the modified nucleotide. At the same time, oxo-εATP did not suppress RNA synthesis by both RNA polymerases in the presence of unmodified nucleotides. Therefore, the oxo-εA modification significantly disrupts nucleotide base pairing during RNA synthesis by RNA polymerases of different classes, and the corresponding nucleotide derivatives cannot be used as potential antiviral or antibacterial transcription inhibitors.