RNA-dependent RNA-polymerase

(noun)

(RdRP, or RNA replicase) 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.

Related Terms

Examples of RNA-dependent RNA-polymerase in the following topics:

  • Viral Replication and Gene Expression

    • RNA viruses are classified into distinct groups depending on their genome and mode of replication.
    • Viruses that replicate via RNA intermediates need an RNA-dependent RNA-polymerase to replicate their RNA, but animal cells do not seem to possess a suitable enzyme.
    • Therefore, this type of animal RNA virus needs to code for an RNA-dependent RNA polymerase.
    • One of these includes RNA-dependent RNA polymerase (RNA replicase), which copies the viral RNA to form a double-stranded replicative form, in turn this directs the formation of new virions.
    • Uncoating of the viral RNA is mediated by receptor-dependent destabilization of the virus capsid (2).

  • Replicative Cycle of Influenza A

    • Delivering the genome to a site where it can produce new copies of viral proteins and RNA
    • The viral RNA (vRNA) molecules, accessory proteins, and RNA-dependent RNA polymerase are then released into the cytoplasm (Step 2 in figure).
    • These core proteins and vRNA form a complex that is transported into the cell nucleus, where the RNA-dependent RNA polymerase begins transcribing complementary positive-sense vRNA (Steps 3a and b in figure).
    • Other viral proteins have multiple actions in the host cell—including degrading cellular mRNA and using the released nucleotides for vRNA synthesis, and also inhibiting translation of host-cell mRNAs.
    • Negative-sense vRNAs that form the genomes of future viruses, RNA-dependent RNA polymerase, and other viral proteins are assembled into a virion.

  • Negative-Strand RNA Viruses of Animals

    • Negative-strand RNA viruses are single-stranded viruses that can infect several types of animals.
    • Animal RNA viruses can be classified according to the sense or polarity of their RNA into negative-sense, positive-sense, or ambisense RNA viruses.
    • The RNA found in a negative-sense virus is not infectious by itself, as it needs to be transcribed into positive-sense RNA.
    • This RNA negative-strand to positive-strand copying is carried out by an RNA-dependent RNA-polymerase.
    • Each virion that has one negative-strand copy can be transcribed to several positive-sense RNAs.

  • RNA Bacteriophages

    • Of these, only two families have RNA genomes: Cystoviridae (segmented dsRNA) and Leviviridae (linear ssRNA).
    • Cystovirus is a genus of dsRNA virus that infect certain Gram-negative bacteria.
    • It has a three-part, segmented, double-stranded RNA genome, totalling ~13.5 kb in length.
    • RNA-dependent RNA polymerases (RdRPs) are critical components in the life cycle of double-stranded RNA (dsRNA) viruses.
    • The recombinant Φ6 RdRP is highly active in vitro, possesses RNA replication and transcription activities, and is capable of using both homologous and heterologous RNA molecules as templates.

  • Initiation of Transcription in Eukaryotes

    • Eukaryotic transcription is carried out in the nucleus of the cell by one of three RNA polymerases, depending on the RNA being transcribed, and proceeds in three sequential stages:
    • RNA polymerase I synthesizes all of the rRNAs except for the 5S rRNA molecule.
    • RNA polymerase III is also located in the nucleus.
    • This polymerase transcribes a variety of structural RNAs that includes the 5S pre-rRNA, transfer pre-RNAs (pre-tRNAs), and small nuclear pre-RNAs.
    • Not all miRNAs are transcribed by RNA Polymerase II, RNA Polymerase III transcribes some of them.

  • The Protein Synthesis Machinery

    • The tRNA molecules are transcribed by RNA polymerase III.
    • Depending on the species, 40 to 60 types of tRNAs exist in the cytoplasm.
    • In eukaryotes, tRNA mole are transcribed from tRNA genes by RNA polymerase III.
    • Depending on the species, 40 to 60 types of tRNAs exist in the cytoplasm.
    • The process of pre-tRNA synthesis by RNA polymerase III only creates the RNA portion of the adaptor molecule.

  • Viral Identification

    • Most DNA viruses are entirely dependent on the host cell's DNA and RNA synthesizing machinery and RNA processing machinery; however, viruses with larger genomes may encode much of this machinery themselves.
    • RNA viruses can be placed into four different groups, depending on their modes of replication.
    • The polarity of single-stranded RNA viruses largely determines the replicative mechanism, depending on whether or not it can be used directly by ribosomes to make proteins.
    • Both types use a reverse transcriptase, or RNA-dependent DNA polymerase enzyme, to carry out the nucleic acid conversion.
    • The Baltimore classification developed by David Baltimore is a virus classification system that groups viruses into families, depending on their type of genome (DNA, RNA, single-stranded (ss), double-stranded (ds), etc.) and their method of replication.

  • Elongation and Termination in Prokaryotes

    • The dissociation of σ allows the core RNA polymerase enzyme to proceed along the DNA template, synthesizing mRNA in the 5' to 3' direction at a rate of approximately 40 nucleotides per second.
    • Since the base pairing between DNA and RNA is not stable enough to maintain the stability of the mRNA synthesis components, RNA polymerase acts as a stable linker between the DNA template and the nascent RNA strands to ensure that elongation is not interrupted prematurely.
    • Depending on the gene being transcribed, there are two kinds of termination signals: one is protein-based and the other is RNA-based.
    • Rho-dependent termination is controlled by the rho protein, which tracks along behind the polymerase on the growing mRNA chain.
    • During elongation, the prokaryotic RNA polymerase tracks along the DNA template, synthesizes mRNA in the 5' to 3' direction, and unwinds and rewinds the DNA as it is read.

  • Elongation and Termination in Eukaryotes

    • RNA Polymerase II will continue to elongate the newly-synthesized RNA until transcription terminates.
    • RNA Polymerase II is a complex of 12 protein subunits.
    • The tRNA, 5S rRNA, and structural RNAs genes transcribed by RNA Polymerase III have a not-entirely-understood termination signal.
    • The RNAs transcribed by RNA Polymerase III have a short stretch of four to seven U's at their 3' end.
    • Xrn2 will start digesting the non-released portion of the newly synthesized RNA until Xrn2 reaches the RNA Polymerase, where it aids in displacing the RNA Polymerase from the template DNA strand.

  • Small Regulatory RNAs

    • Small regulatory RNAs encompass a specific class of RNAs that affect gene regulation.
    • Antisense RNAs are used to bind to complementary mRNAs and inhibit protein translation.
    • The antisense RNAs are categorized as small regulatory RNAs due to their small size.
    • House-keeping RNAs identified to date include rRNA and tRNAs. rRNAs that are considered to be house-keeping genes can bind to RNA polymerases and regulate transcription or function in larger complexes that are required for protein secretion or synthesis processes.
    • The antisense RNA can bind to the mRNA and inhibit translation.