Replicases

Replicase is an enzyme or protein complex that catalyzes the replication of genetic material. The term is used in virology to describe the RNA-dependent RNA polymerase and associated replication proteins that copy a viral RNA genome, and in plasmid biology to describe initiator proteins that trigger plasmid DNA replication. In RNA viruses, the replicase is typically encoded by the viral genome and forms part of a larger replication complex that copies the viral RNA.

In RNA viruses, the replicase enzyme copies the genomic RNA to produce new genomes and subgenomic RNAs. Replication often occurs in membrane-bound replication complexes that assemble from viral nonstructural proteins and host cell factors. These complexes can be error-prone, contributing to the high mutation rates seen in RNA viruses. The replicase machinery may include helicase activities and other cofactors that aid in unwinding RNA and regulating replication.

In plasmid biology, replicases generally refer to initiator proteins (Rep proteins) that recognize the origin of replication on the plasmid DNA and initiate replication. They often nick one strand at the origin to create a primer for DNA synthesis and recruit host or plasmid-encoded polymerases. Rep protein activity is usually tightly regulated to control plasmid copy number and ensure stable inheritance during cell division. Different plasmids employ diverse Rep families with specific origins and regulation mechanisms.

In eukaryotic organelles, genome replication is carried out by specialized DNA polymerases and associated factors rather than by proteins typically described as replicases; the term is more commonly used in viral and plasmid contexts. Across systems, replicases are central to genome propagation and genetic diversity.