T.11 Terminación
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Questions and Answers

What does the torpedo require to disassociate the remaining RNA from the DNA polymerase?

  • A DNA polymerase activity
  • A RNA helicase activity (correct)
  • A RNA polymerase activity
  • A DNA ligase activity

    • What happens to the polymerase when the torpedo reaches it?

  • It continues to transcribe the DNA
  • It undergoes an allosteric change and releases the RNA (correct)
  • It becomes inactive and stops transcription
  • It degrades the RNA and releases the RNA polymerase

    • What is the function of the PAP-binding protein (PABP)?

  • To initiate transcription
  • To add a poly(A) tail to the RNA
  • To digest the RNA
  • To cover and stabilize the poly(A) tail (correct)

    • What is the characteristic of the phosphorylation pattern of the CTD during elongation?

    <p>Phosphorylation of Ser2, Tyr1, and Thr4</p> Signup and view all the answers

    What is unique about the termination mechanism of histone mRNAs?

    <p>It does not involve polyadenylation</p> Signup and view all the answers

    What happens when the RNA polymerase reaches the terminator sequences at the end of the gene?

    <p>It releases the DNA and goes back to the promoter to reinitiate transcription</p> Signup and view all the answers

    What is the role of the protein TTF1 in the termination of RNA Pol I?

    <p>It recognizes a secondary structure in the RNA transcript and pauses the RNA polymerase</p> Signup and view all the answers

    What is the function of the exonucleases Xrn2 in the termination of RNA Pol I?

    <p>It degrades the RNA transcript from 5' to 3'</p> Signup and view all the answers

    What is the role of the complex CPSF, CFI, CFII, and PAP in the termination of RNA Pol II?

    <p>It cleaves the RNA transcript and adds a poly(A) tail</p> Signup and view all the answers

    What is the function of the mechanism of torpedo in RNA Pol I and RNA Pol II?

    <p>It degrades the RNA transcript from 5' to 3' and releases the paused RNA polymerase</p> Signup and view all the answers

    What is the characteristic of bacterial termination?

    <p>The last nucleotide introduced by the RNA polymerase is the last nucleotide of the 3' region it copied</p> Signup and view all the answers

    What is unique about the RNA Pol III compared to other polymerases?

    <p>It has a higher capacity for initiation and termination</p> Signup and view all the answers

    What happens to the RNA downstream of the cleavage site in eukaryotic RNA Pol I and II?

    <p>It is degraded into smaller pieces and does not form part of the final RNA</p> Signup and view all the answers

    What is the role of the trimer C82/C34/C31 in RNA Pol III?

    <p>It facilitates the process of termination and reinitiation</p> Signup and view all the answers

    What is the result of the cleavage event in eukaryotic RNA Pol I and II?

    <p>The formation of a primary transcript with a 3' end</p> Signup and view all the answers

    What is the primary function of the complex formed by Nrd1, Nab3, and Sen1 in non-coding RNA (ncRNA) transcription?

    <p>To recognize and bind to specific sequences in the ncRNA</p> Signup and view all the answers

    What happens to the RNA polymerase II when it reaches a region that obliges it to pause temporarily during ncRNA transcription?

    <p>The helicase Sen1 acts to release the RNA polymerase II, terminating transcription</p> Signup and view all the answers

    What is the characteristic of the ncRNA transcripts that are recognized by the Nrd1 and Nab3 proteins?

    <p>They have a specific sequence characteristic of non-coding RNAs</p> Signup and view all the answers

    What is the fate of the ncRNA transcript when the RNA polymerase II is paused in a region where it should not be transcribing?

    <p>It is degraded by the exosome</p> Signup and view all the answers

    What is the role of the helicase Sen1 in the termination of ncRNA transcription?

    <p>It releases the RNA polymerase II, terminating transcription</p> Signup and view all the answers

    What happens to mRNAs that experience premature termination?

    <p>They are degraded by the exosome and TRAMP complex.</p> Signup and view all the answers

    What is required for premature termination to occur?

    <p>Presence of Nrd1 and Nab3 and unphosphorylated CTD.</p> Signup and view all the answers

    What happens to transcripts that start at the correct site?

    <p>They are elongated and can reach the polyadenylation site.</p> Signup and view all the answers

    What is the fate of aberrant or antisense transcripts?

    <p>They are rapidly detected by the NNS and TRAMP systems and degraded.</p> Signup and view all the answers

    What is the primary difference between bacterial termination and eukaryotic RNA Pol I and II termination?

    <p>The cleavage of the RNA transcript</p> Signup and view all the answers

    What is the role of the trimer C82/C34/C31 in RNA Pol III?

    <p>To facilitate the termination and re-initiation process</p> Signup and view all the answers

    What happens to the RNA downstream of the cleavage site in eukaryotic RNA Pol I and II?

    <p>It is degraded into smaller pieces</p> Signup and view all the answers

    What is the characteristic of the RNA Pol III compared to other polymerases?

    <p>It has a higher capacity for rapid initiation and termination</p> Signup and view all the answers

    What is the result of the cleavage event in eukaryotic RNA Pol I and II?

    <p>The generation of a 3' end of the RNA transcript</p> Signup and view all the answers

    What is the primary function of the endonuclease Rnt1 in RNA Pol I termination?

    <p>To introduce a cut in the transcript, generating a 3' end</p> Signup and view all the answers

    What is the role of the complex formed by CPSF, CFI, and CFII in RNA Pol II termination?

    <p>To introduce a cut in the transcript, generating a 3' end</p> Signup and view all the answers

    What is the function of the exonuclease Xrn2 in RNA Pol I termination?

    <p>To degrade the remaining RNA downstream of the cleavage site</p> Signup and view all the answers

    What is the characteristic of the torpedo mechanism in RNA Pol I and II termination?

    <p>It degrades the remaining RNA downstream of the cleavage site</p> Signup and view all the answers

    What happens to the RNA polymerase II when it reaches the terminator sequences at the end of the gene?

    <p>It is released from the DNA and can initiate a new cycle of elongation</p> Signup and view all the answers

    What is the main difference between the torpedo model and the allosteric model of transcription termination?

    <p>The torpedo model involves the degradation of the RNA polymerase, while the allosteric model involves a change in the polymerase's conformation.</p> Signup and view all the answers

    What is the main function of the complex formed by Nrd1, Nab3, and Sen1 in non-coding RNA (ncRNA) transcription?

    <p>To terminate transcription of ncRNAs</p> Signup and view all the answers

    What happens to the RNA polymerase II when it reaches a region that obliges it to pause temporarily during ncRNA transcription?

    <p>It dissociates from the DNA template</p> Signup and view all the answers

    Which of the following factors is NOT involved in the cleavage and polyadenylation of RNA Pol II transcripts?

    <p>PAP-binding protein</p> Signup and view all the answers

    What is unique about the phosphorylation pattern of the CTD during the transcription of ncRNAs?

    <p>It has a distinct pattern that differs from mRNA transcription</p> Signup and view all the answers

    What is the characteristic of the phosphorylation pattern of the CTD during the initiation of transcription?

    <p>Phosphorylation of Ser5 and sometimes Ser</p> Signup and view all the answers

    What is the role of the Glc7 protein in the termination of RNA Pol II transcription?

    <p>It is a protein phosphatase that removes the phosphorylation of Tyr1, allowing for termination.</p> Signup and view all the answers

    What is the fate of the ncRNA transcript when the RNA polymerase II is paused in a region where it should not be transcribing?

    <p>It is degraded by the exosome</p> Signup and view all the answers

    What is the characteristic of the ncRNA transcripts that are recognized by the Nrd1 and Nab3 proteins?

    <p>They have a specific sequence motif</p> Signup and view all the answers

    What is the characteristic of the termination mechanism of histone mRNAs?

    <p>It does not involve the cleavage and polyadenylation of the RNA transcript.</p> Signup and view all the answers

    What is the primary reason for the degradation of transcripts that are not structured and are released from the RNA polymerase?

    <p>They are marked for degradation by the TRAMP complex</p> Signup and view all the answers

    What is the characteristic of transcripts that are recognized by the Nrd1 and Nab3 proteins?

    <p>They lack a reading pattern</p> Signup and view all the answers

    What is the fate of transcripts that are initiated at the correct site and continue to elongate?

    <p>They are extended to the polyadenylation site (PAS)</p> Signup and view all the answers

    What is the characteristic of the termination mechanism of histone mRNAs?

    <p>It involves a cutting mechanism but not polyadenylation</p> Signup and view all the answers

    What is the role of the NNS complex in the regulation of transcription?

    <p>It is involved in the termination of transcription</p> Signup and view all the answers

    Study Notes

    Transcription Termination

    • Transcription termination is the process by which RNA polymerase dissociates from the DNA template, and it involves the release of the RNA transcript.
    • There are different termination mechanisms for bacterial RNA polymerase and eukaryotic RNA polymerase.

    Bacterial RNA Polymerase

    • In bacterial RNA polymerase, termination occurs when the polymerase reaches a terminator region, which induces the release of the RNA transcript.
    • The last nucleotide introduced by the RNA polymerase is the last nucleotide of the 3' region copied.

    Eukaryotic RNA Polymerase

    • In eukaryotic RNA polymerase, there are three types of RNA polymerase: RNA Pol I, RNA Pol II, and RNA Pol III.
    • Each type of RNA polymerase has a different termination mechanism.

    RNA Pol III

    • RNA Pol III is responsible for transcribing short genes.
    • Termination in RNA Pol III involves the presence of a C82/C34/C31 trimer, which facilitates termination and reinitiation.
    • The polymerase is loosely bound to the DNA template during transcription and becomes tightly bound during termination.
    • The C37 subunit transmits termination signals, releasing the DNA upstream and liberating the polymerase.

    RNA Pol I

    • RNA Pol I is responsible for transcribing ribosomal RNA.
    • Termination in RNA Pol I involves the binding of a protein called TTF1 (or Reb1) to the DNA, pausing the polymerase.
    • An endonuclease called Rnt1 cleaves the RNA, and the remaining RNA is degraded by an exonuclease called Xrn2, releasing the polymerase.

    RNA Pol II

    • RNA Pol II is responsible for transcribing messenger RNA (mRNA).
    • Termination in RNA Pol II involves the recognition of specific sequences (e.g., AAUAAA and GU-rich sequences) by a complex of proteins, including CPSF, CstF, and the poly(A) polymerase.
    • The complex cleaves the RNA, and the poly(A) polymerase adds a poly(A) tail to the RNA.
    • The torpedo mechanism involves the degradation of the RNA downstream of the cleavage site, releasing the polymerase.

    Unified Model of Termination

    • The unified model of termination combines elements of the allosteric and torpedo models.
    • The torpedo mechanism induces a conformational change in the polymerase, releasing it from the DNA template.

    Alternative Forms of Termination

    • There are alternative forms of termination in eukaryotes, such as the formation of the 3' end of histone mRNAs.
    • These mechanisms do not involve polyadenylation and are specific to certain genes.
    • Non-coding RNAs (ncRNAs) also have distinct termination mechanisms, which involve the binding of specific proteins to the RNA.

    ncRNA Termination

    • ncRNA termination involves the binding of proteins Nrd1, Nab3, and Sen1 to the RNA and the polymerase.
    • The helicase Sen1 dissociates the polymerase from the DNA, terminating transcription.
    • This mechanism can also occur when the polymerase pauses or encounters an obstacle, leading to the degradation of the transcript.

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