Viral polymerases.

Viral polymerases play a central role in viral genome replication and transcription. Based on the genome type and the specific needs of particular virus, RNA-dependent RNA polymerase, RNA-dependent DNA polymerase, DNA-dependent RNA polymerase, and DNA-dependent RNA polymerases are found in various viruses. Viral polymerases are generally active as a single protein capable of carrying out multiple functions related to viral genome synthesis. Specifically, viral polymerases use variety of mechanisms to recognize initial binding sites, ensure processive elongation, terminate replication at the end of the genome, and also coordinate the chemical steps of nucleic acid synthesis with other enzymatic activities. This review focuses on different viral genome replication and transcription strategies, and the polymerase interactions with various viral proteins that are necessary to complete genome synthesis.