RNA polymerase plays a vital role in genome replication and transcription in viruses. RNA-dependent RNA polymerases and reverse transcriptases are unique to viruses since the host cell does not require the RNA replication or reverse transcription.

RNA polymerase in RNA viruses has a very high error rate because of the lack of proofreading ability. This lack of proofreading ability renders RNA polymerases incapable of correcting any mistakes they make. As a result, the mutations remain in the newly synthesized RNA. The high error rate explains why RNA viruses are so successful and how they evolve so readily.