RNA polymerase

Biology

(noun)

a DNA-dependent RNA polymerase, an enzyme, that produces RNA

Related Terms

  • operon
  • promoter
Microbiology

(noun)

An enzyme responsible for the synthesis of RNA during transcription.

Examples of RNA polymerase in the following topics:

  • 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.
  • Initiation of Transcription in Eukaryotes

    • RNA polymerase I synthesizes all of the rRNAs except for the 5S rRNA molecule.
    • RNA polymerase II is located in the nucleus and synthesizes all protein-coding nuclear pre-mRNAs.
    • 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 Promoter and the Transcription Machinery

    • RNA polymerase binds to the transcription initiation complex, allowing transcription to occur.
    • Once this transcription initiation complex is assembled, RNA polymerase can bind to its upstream sequence.
    • When bound along with the transcription factors, RNA polymerase is phosphorylated.
    • A generalized promoter of a gene transcribed by RNA polymerase II is shown.
    • RNA polymerase II then binds and forms the transcription initiation complex.
  • Initiation of Transcription in Prokaryotes

    • Prokaryotes use the same RNA polymerase to transcribe all of their genes.
    • Each subunit has a unique role: the two α-subunits are necessary to assemble the polymerase on the DNA; the β-subunit binds to the ribonucleoside triphosphate that will become part of the nascent "recently-born" mRNA molecule; and the β' binds the DNA template strand.
    • It confers transcriptional specificity such that the polymerase begins to synthesize mRNA from an appropriate initiation site.
    • The polymerase comprised of all five subunits is called the holoenzyme.
    • The σ subunit of prokaryotic RNA polymerase recognizes consensus sequences found in the promoter region upstream of the transcription start sight.
  • 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.
    • Rho-dependent termination is controlled by the rho protein, which tracks along behind the polymerase on the growing mRNA chain.
    • This, coupled with the stalled polymerase, induces enough instability for the core enzyme to break away and liberate the new mRNA transcript.
    • 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.
  • 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).
  • 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.
  • mRNA Processing

    • While RNA Polymerase II is still transcribing downstream of the proper end of a gene, the pre-mRNA is cleaved by an endonuclease-containing protein complex between an AAUAAA consensus sequence and a GU-rich sequence.
    • This releases the functional pre-mRNA from the rest of the transcript, which is still attached to the RNA Polymerase.
    • An enzyme called poly (A) polymerase (PAP) is part of the same protein complex that cleaves the pre-mRNA and it immediately adds a string of approximately 200 A nucleotides, called the poly (A) tail, to the 3' end of the just-cleaved pre-mRNA.
    • Poly (A) Polymerase adds a 3' poly (A) tail to the pre-mRNA.
    • The pre-mRNA is cleaved off the rest of the growing transcript before RNA Polymerase II has stopped transcribing.
  • The Protein Synthesis Machinery

    • Protein synthesis, or translation of mRNA into protein, occurs with the help of ribosomes, tRNAs, and aminoacyl tRNA synthetases.
    • The tRNA molecules are transcribed by RNA polymerase III.
    • The transfer RNAs (tRNAs) are structural RNA molecules.
    • In eukaryotes, tRNA mole are transcribed from tRNA genes by RNA polymerase III.
    • The process of pre-tRNA synthesis by RNA polymerase III only creates the RNA portion of the adaptor molecule.
  • 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.
Subjects
  • Accounting
  • Algebra
  • Art History
  • Biology
  • Business
  • Calculus
  • Chemistry
  • Communications
  • Economics
  • Finance
  • Management
  • Marketing
  • Microbiology
  • Physics
  • Physiology
  • Political Science
  • Psychology
  • Sociology
  • Statistics
  • U.S. History
  • World History
  • Writing

Except where noted, content and user contributions on this site are licensed under CC BY-SA 4.0 with attribution required.