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Questions and Answers
What does the torpedo require to disassociate the remaining RNA from the DNA polymerase?
What happens to the polymerase when the torpedo reaches it?
What is the function of the PAP-binding protein (PABP)?
What is the characteristic of the phosphorylation pattern of the CTD during elongation?
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What is unique about the termination mechanism of histone mRNAs?
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What happens when the RNA polymerase reaches the terminator sequences at the end of the gene?
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What is the role of the protein TTF1 in the termination of RNA Pol I?
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What is the function of the exonucleases Xrn2 in the termination of RNA Pol I?
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What is the role of the complex CPSF, CFI, CFII, and PAP in the termination of RNA Pol II?
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What is the function of the mechanism of torpedo in RNA Pol I and RNA Pol II?
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What is the characteristic of bacterial termination?
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What is unique about the RNA Pol III compared to other polymerases?
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What happens to the RNA downstream of the cleavage site in eukaryotic RNA Pol I and II?
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What is the role of the trimer C82/C34/C31 in RNA Pol III?
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What is the result of the cleavage event in eukaryotic RNA Pol I and II?
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What is the primary function of the complex formed by Nrd1, Nab3, and Sen1 in non-coding RNA (ncRNA) transcription?
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What happens to the RNA polymerase II when it reaches a region that obliges it to pause temporarily during ncRNA transcription?
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What is the characteristic of the ncRNA transcripts that are recognized by the Nrd1 and Nab3 proteins?
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What is the fate of the ncRNA transcript when the RNA polymerase II is paused in a region where it should not be transcribing?
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What is the role of the helicase Sen1 in the termination of ncRNA transcription?
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What happens to mRNAs that experience premature termination?
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What is required for premature termination to occur?
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What happens to transcripts that start at the correct site?
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What is the fate of aberrant or antisense transcripts?
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What is the primary difference between bacterial termination and eukaryotic RNA Pol I and II termination?
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What is the role of the trimer C82/C34/C31 in RNA Pol III?
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What happens to the RNA downstream of the cleavage site in eukaryotic RNA Pol I and II?
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What is the characteristic of the RNA Pol III compared to other polymerases?
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What is the result of the cleavage event in eukaryotic RNA Pol I and II?
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What is the primary function of the endonuclease Rnt1 in RNA Pol I termination?
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What is the role of the complex formed by CPSF, CFI, and CFII in RNA Pol II termination?
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What is the function of the exonuclease Xrn2 in RNA Pol I termination?
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What is the characteristic of the torpedo mechanism in RNA Pol I and II termination?
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What happens to the RNA polymerase II when it reaches the terminator sequences at the end of the gene?
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What is the main difference between the torpedo model and the allosteric model of transcription termination?
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What is the main function of the complex formed by Nrd1, Nab3, and Sen1 in non-coding RNA (ncRNA) transcription?
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What happens to the RNA polymerase II when it reaches a region that obliges it to pause temporarily during ncRNA transcription?
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Which of the following factors is NOT involved in the cleavage and polyadenylation of RNA Pol II transcripts?
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What is unique about the phosphorylation pattern of the CTD during the transcription of ncRNAs?
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What is the characteristic of the phosphorylation pattern of the CTD during the initiation of transcription?
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What is the role of the Glc7 protein in the termination of RNA Pol II transcription?
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What is the fate of the ncRNA transcript when the RNA polymerase II is paused in a region where it should not be transcribing?
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What is the characteristic of the ncRNA transcripts that are recognized by the Nrd1 and Nab3 proteins?
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What is the characteristic of the termination mechanism of histone mRNAs?
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What is the primary reason for the degradation of transcripts that are not structured and are released from the RNA polymerase?
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What is the characteristic of transcripts that are recognized by the Nrd1 and Nab3 proteins?
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What is the fate of transcripts that are initiated at the correct site and continue to elongate?
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What is the characteristic of the termination mechanism of histone mRNAs?
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What is the role of the NNS complex in the regulation of transcription?
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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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