Viral RNA-Dependent RNA Polymerases: A Structural Overview

Most emerging and re-emerging human and animal viral diseases are associated with RNA viruses. All these pathogens, with the exception of retroviruses, encode a specialized enzyme called RNA-dependent RNA polymerase (RdRP), which catalyze phosphodiester-bond formation between ribonucleotides (NTPs) in an RNA template-dependent manner. These enzymes function either as single polypeptides or in complex with other viral or host components to transcribe and replicate the viral RNA genome. The structures of RdRPs and RdRP catalytic complexes, currently available for several members of (+) ssRNA, (-)ssRNA and dsRNA virus families, have provided high resolution snapshots of the functional steps underlying replication and transcription of viral RNA genomes and their regulatory mechanisms.