This family represents the RNA-directed RNA polymerase found in many positive strand RNA eukaryotic viruses. Structural studies indicate that these proteins form the "right hand" structure found in all oligonucleotide polymerases, containing thumb, finger and palm domains, and also the additional bridging finger and thumb domains unique to RNA-directed RNA polymerases [1,2,3,4]. Remdesivir, a recent treatment approved for Covid-19 disease, directly interacts with this region of the RdRp (NSP12) from SARS-CoV-2 and explains its mechanism of action via delayed-chain termination [5].

1: RNA Dependent RNA Polymerases: Insights from Structure, Function and Evolution. Venkataraman S, Prasad BVLS, Selvarajan R; Viruses. 2018; [Epub ahead of print] PMID:29439438

2: Structural basis for proteolysis-dependent activation of the poliovirus RNA-dependent RNA polymerase. Thompson AA, Peersen OB; EMBO J. 2004;23:3462-3471. PMID:15306852

3: Structure of the SARS-CoV nsp12 polymerase bound to nsp7 and nsp8 co-factors. Kirchdoerfer RN, Ward AB; Nat Commun. 2019;10:2342. PMID:31138817

4: Structure of replicating SARS-CoV-2 polymerase. Hillen HS, Kokic G, Farnung L, Dienemann C, Tegunov D, Cramer P; Nature. 2020;584:154-156. PMID:32438371

5: Evolution of the SARS-CoV-2 proteome in three dimensions (3D) during the first 6 months of the COVID-19 pandemic. Lubin JH, Zardecki C, Dolan EM, Lu C, Shen Z, Dutta S, Westbrook JD, Hudson BP, Goodsell DS, Williams JK, Voigt M, Sarma V, Xie L, Venkatachalam T, Arnold S, Alfaro Alvarado LH, Catalfano K, Khan A, McCarthy E, Staggers S, Tinsley B, Trudeau A, Singh J, Whitmore L, Zheng H, Benedek M, Currier J, Dresel M, Duvvuru A, Dyszel B, Fingar E, Hennen EM, Kirsch M, Khan AA, Labrie-Cleary C, Laporte S, Lenkeit E, Martin K, Orellana M, Ortiz-Alvarez de la Campa M, Paredes I, Wheeler B, Rupert A, Sam A, See K, Soto Zapata S, Craig PA, Hall BL, Jiang J, Koeppe JR, Mills SA, Pikaart MJ, Roberts R, Bromberg Y, Hoyer JS, Duffy S, Tischfield J, Ruiz FX, Arnold E, Baum J, Sandberg J, Brannigan G, Khare SD, Burley SK; Proteins. 2021; [Epub ahead of print] PMID:34580920