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Replicase

RNA-dependent RNA polymerase
RNA Replicase structure.png
RNA Replicase structure PDB: 3PHU​.
Identifiers
EC number 2.7.7.48
CAS number 9026-28-2
Databases
IntEnz IntEnz view
BRENDA BRENDA entry
ExPASy NiceZyme view
KEGG KEGG entry
MetaCyc metabolic pathway
PRIAM profile
PDB structures RCSB PDB PDBe PDBsum
Gene Ontology AmiGO / EGO
RNA dependent RNA polymerase
Identifiers
Symbol RdRP_1
Pfam PF00680
Pfam clan CL0027
InterPro IPR001205
SCOP 2jlg
SUPERFAMILY 2jlg
RNA-directed RNA polymerase, flaviviral
Identifiers
Symbol RNA_pol_flaviviral
Pfam PF00972
InterPro IPR000208

RNA-dependent RNA polymerase (RdRP), (RDR), or RNA replicase, is an enzyme that catalyzes the replication of RNA from an RNA template. This is in contrast to a typical DNA-dependent RNA polymerase, which catalyzes the transcription of RNA from a DNA template.

RNA-dependent RNA polymerase (RdRp) is an essential protein encoded in the genomes of all RNA-containing viruses with no DNA stage i.e. only RNA viruses. It catalyses synthesis of the RNA strand complementary to a given RNA template. The RNA replication process is a two-step mechanism. First, the initiation step of RNA synthesis begins at or near the 3' end of the RNA template by means of a primer-independent (de novo), or a primer-dependent mechanism that utilizes a viral protein genome-linked (VPg) primer. The de novo initiation consists in the addition of a nucleoside triphosphate (NTP) to the 3'-OH of the first initiating NTP. During the following so-called elongation phase, this nucleotidyl transfer reaction is repeated with subsequent NTPs to generate the complementary RNA product.

Viral RdRPs were discovered in the early 1960s from studies on mengovirus and polio virus when it was observed that these viruses were not sensitive to actinomycin D, a drug that inhibits cellular DNA-directed RNA synthesis. This lack of sensitivity suggested that there is a virus-specific enzyme that could copy RNA from an RNA template and not from a DNA template.

The most famous example of RdRP is that of the polio virus. The viral genome is composed of RNA, which enters the cell through receptor-mediated endocytosis. From there, the RNA is able to act as a template for complementary RNA synthesis, immediately. The complementary strand is then, itself, able to act as a template for the production of new viral genomes that are further packaged and released from the cell ready to infect more host cells. The advantage of this method of replication is that there is no DNA stage; replication is quick and easy. The disadvantage is that there is no 'back-up' DNA copy.


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Wikipedia

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