RNA polymerase

(noun)

An enzyme responsible for the synthesis of RNA during transcription.

Examples of RNA polymerase in the following topics:

  • Verrucomicrobia

    • Support for this superphylum has been found by examining the RNA polymerase protein RpoB.
    • rpoB is the gene that encodes the β subunit of bacterial RNA polymerase.
    • Cavalier-Smith has postulated that the Verrucomicrobia belong in the clade Planctobacteria in the larger clade Gracilicutes. 16S rRNA data corroborate that view.
    • RNA polymerase II (also called RNAP II and Pol II) is an enzyme found in eukaryotic cells.
    • It catalyzes the transcription of DNA to synthesize precursors of mRNA and most snRNA and microRNA.

  • Control of Transcription in Archaea

    • Other characteristic archaean features are the organization of genes of related function—such as enzymes that catalyze steps in the same metabolic pathway into novel operons, and large differences in tRNA genes and their aminoacyl tRNA synthetases.
    • Transcription and translation in archaea resemble these processes in eukaryotes more than in bacteria, with the archaean RNA polymerase and ribosomes being very close to their equivalents in eukaryotes.
    • Although archaea only have one type of RNA polymerase, its structure and function in transcription seems to be close to that of the eukaryotic RNA polymerase II, with similar protein assemblies (the general transcription factors) directing the binding of the RNA polymerase to a gene's promoter.
    • Post-transcriptional modification is simpler than in eukaryotes, since most archaean genes lack introns, although there are many introns in their transfer RNA and ribosomal RNA genes, and introns may occur in a few protein-encoding genes.

  • Regulation of Sigma Factor Activity

    • Specifically, in bacteria, sigma factors are necessary for recognition of RNA polymerase to the gene promoter site.
    • The sigma factor allows the RNA polymerase to properly bind to the promoter site and initiate transcription which will result in the production of an mRNA molecule.
    • Once the role of the sigma factor is completed, the protein leaves the complex and RNA polymerase will continue with transcription.
    • The anti-sigma factors will bind to the RNA polymerase and prevent its binding to sigma factors present at the promoter site.

  • Viral Replication and Gene Expression

    • 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.
    • No viral proteins can be made until viral messenger RNA is available; thus, the nature of the RNA in the virion affects the strategy of the virus: In plus-stranded RNA viruses, the virion (genomic) RNA is the same sense as mRNA and so functions as mRNA.
    • 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.
    • The positive-sense RNA serves as template for complementary negative-strand synthesis, thereby producing a double-stranded RNA (replicative form, RF) (5).

  • 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.

  • 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.

  • 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.

  • Primer Extension Analysis

    • Primer extension is used to map the 5' ends of DNA or RNA fragments.
    • Primer extension is a technique whereby the 5' ends of RNA or DNA can be mapped.
    • The primer is allowed to anneal to the RNA and reverse transcriptase is used to synthesize cDNA from the RNA until it reaches the 5' end of the RNA.
    • In one, the modified nucleotide cannot be recognized by the polymerase or reverse transcriptase; in such cases, the chain ends at the site of modification.
    • This is a diagram of transcription initiation by the RNA polymerase.

  • 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.

  • Viral Identification

    • Both types use a reverse transcriptase, or RNA-dependent DNA polymerase enzyme, to carry out the nucleic acid conversion.
    • Reoviruses)IV: (+)ssRNA viruses (+)sense RNA (e.g.
    • Picornaviruses, Togaviruses)V: (−)ssRNA viruses (−)sense RNA (e.g.
    • VI: ssRNA-RT viruses (+)sense RNA with DNA intermediate in life-cycle (e.g.
    • An example of Baltimore Virus classification I: dsDNA virusesII: ssDNA virusesIII: dsRNA virusesIV: (+)ssRNA virusesV: (−)ssRNA virusesVI: ssRNA-RT virusesVII: dsDNA-RT viruses