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.

  • Inhibiting Nucleic Acid Synthesis

    • Antimicrobial drugs can target nucleic acid (either RNA or DNA) synthesis.
    • For example, the antimicrobial rifampin binds to DNA-dependent RNA polymerase, thereby inhibiting the initiation of RNA transcription.
    • In addition to DNA polymerase, the enzyme that synthesizes the new DNA by adding nucleotides matched to the template strand, a number of other proteins are associated with the fork and assist in the initiation and continuation of DNA synthesis.
    • RNA Polymerase, an enzyme that produces RNA, from T. aquaticus pictured during elongation.
    • Portions of the enzyme were made transparent so as to make the path of RNA and DNA more clear.

  • 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.

  • 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.

  • Viroids

    • The replication mechanism involves RNA polymerase II, an enzyme normally associated with synthesis of messenger RNA from DNA, which instead catalyzes "rolling circle" synthesis of new RNA using the viroid's RNA as template.
    • Virusoids are circular single-stranded RNAs dependent on plant viruses for replication and encapsidation.
    • Since they depend on helper viruses, they are classified as satellites.
    • Pospiviroidae replication occurs in an asymmetric fashion via host cell RNA polymerase, RNase, and RNA ligase.
    • It is thought the positive RNA strand acts as a template to form negative strands with the help of an enzyme thought to be RNA polymerase II.

  • Positive-Strand RNA Viruses of Animals

    • Positive strand RNA viruses are the single largest group of RNA viruses with 30 families.
    • Single stranded RNA viruses can be classified according to the sense or polarity of their RNA into negative-sense and positive-sense, or ambisense RNA viruses.
    • Positive-sense viral RNA is similar to mRNA and thus can be immediately translated by the host cell.
    • Negative-sense viral RNA is complementary to mRNA and thus must be converted to positive-sense RNA by an RNA polymerase before translation.
    • The genome RNA is unusual because it has a protein on the 5' end that is used as a primer for transcription by RNA polymerase.

  • Prokaryotic Transcription and Translation Are Coupled

    • RNA polymerase (RNAP) binds to one of several specificity factors, σ, to form a holoenzyme.
    • The RNA polymerase transcribes the DNA (the beta subunit initiates the synthesis), but produces about 10 abortive (short, non-productive) transcripts which are unable to leave the RNA polymerase because the exit channel is blocked by the σ-factor.The σ-factor eventually dissociates from the holoenzyme, and elongation proceeds.
    • Promoter strength is in many (but not all) cases, a matter of how tightly RNA polymerase and its associated accessory proteins bind to their respective DNA sequences.
    • Two termination mechanisms are well known: Intrinsic termination (also called Rho-independent transcription termination) involves terminator sequences within the RNA that signal the RNA polymerase to stop.
    • Rho-dependent termination uses a termination factor called ρ factor(rho factor) which is a protein to stop RNA synthesis at specific sites.