Naming: By convention viral polymerases are called RNA/DNA-dependent whereas cellular polymerases are called RNA/DNA-directed.
- RNA 3'OH (Retroviridae, LTR retrotransposons, Caulimoviridae, Hepadnaviridae)
- DNA 3'OH (LINE, SINE)
- RTase at Tyr-OH residue (Caulimoviridae, Hepadnaviridae)
- a Guanosine 2'OH in retron mRNA (Retrons)
- DNA nucleotidyltransferase (RNA-dependent) EC:22.214.171.124 RHEA:22508
Mechanism Viral Rtase are characterized by a conserved motif in which two conserved aspartic acid residues are bound to two magnesium ions. The reaction begins with the deprotonation of primer's 3' OH, in a manner that doesn't require a base . Subsequently, the 3'-oxygen acts as a nucleophile to attack the phosphate bond and eventually releases a pyrophosphate.