RNAdependent

RNA-dependent is an adjective used in molecular biology to describe enzymes or processes that use RNA as a template or substrate to synthesize RNA. The term is most commonly encountered in reference to RNA-dependent RNA polymerases, a class of enzymes that catalyze RNA synthesis using an RNA template.

RNA-dependent RNA polymerases (RdRPs) are central to the replication of RNA viruses, which lack a DNA stage in their life cycles. Viral RdRPs copy the viral RNA genome and often generate subgenomic RNAs necessary for viral protein production. They typically contain conserved catalytic motifs and operate with a palm-domain structure, using metal ions to drive polymerization and generally propagating RNA synthesis in the 5' to 3' direction. RdRPs are known for relatively high error rates, contributing to rapid viral evolution.

In addition to viral roles, RNA-dependent RNA polymerases participate in RNA silencing pathways in some eukaryotes, fungi, and plants. These RdRPs amplify silencing signals by converting aberrant or single-stranded RNA into double-stranded RNA, which is then processed into small interfering RNAs. Plants harbor several RdRPs, such as RDR1, RDR2, and RDR6, each contributing to antiviral defense and gene regulation; in the fungus Neurospora crassa, QDE-1 is a well-studied RdRP involved in quelling.

The study of RdRPs encompasses structure, catalysis, and evolution. They are a notable exception to the general absence of RNA-templated polymerases in many organisms, and they are important targets in antiviral research due to their essential role in RNA virus replication and their distinct catalytic mechanisms.