6 Questions
What is the primary function of general transcription factors during transcription initiation?
To recruit RNA polymerase II to the promoter region
Which subunit of RNA polymerase II contains the active site for RNA synthesis?
Rpb1
What is the primary function of core promoters in transcription initiation?
To serve as binding sites for RNA polymerase II and general transcription factors
During the elongation process, in which direction does RNA polymerase II read the template DNA strand?
3' → 5'
What is the primary function of transcriptional elongation factors during the elongation process?
To facilitate RNAP II processivity and pause sites
What is the primary mechanism of transcription termination in eukaryotes?
Termination occurs when RNAP II encounters a terminator sequence in the template DNA
Study Notes
Transcription Initiation
- RNA polymerase II (RNAPII) is recruited to the promoter region through the interaction of transcription factors with specific DNA sequences
- General transcription factors (GTFs) such as TFIIA, TFIIB, TFIID, TFIIE, and TFIIH bind to the promoter region and facilitate RNAPII recruitment
- The pre-initiation complex (PIC) is formed, consisting of RNAPII, GTFs, and other factors
RNA Polymerase II Structure
- RNAPII is a large enzyme complex composed of 12 subunits (Rpb1-12)
- Rpb1 contains the active site for RNA synthesis and is the largest subunit
- Rpb2 is involved in RNA synthesis and proofreading
- Rpb3-12 are smaller subunits that stabilize the complex and facilitate transcription
Promoter Recognition
- Promoters are specific DNA sequences that serve as binding sites for RNAPII and GTFs
- Core promoters are the minimal elements necessary for RNAPII recruitment, typically located 30-100 bp upstream of the transcription start site
- Proximal promoters are located near the transcription start site, while distal promoters are located farther upstream
- Enhancers are distant regulatory elements that loop back to the promoter to enhance transcription
Elongation Process
- After initiation, RNAPII begins transcribing the template DNA strand
- RNAPII reads the template strand in a 3' → 5' direction, synthesizing RNA in a 5' → 3' direction
- The RNA-DNA hybrid is maintained during transcription, with the RNA strand being displaced from the template strand
- Transcriptional elongation factors (TEFs) such as TFIIS and TFIIF facilitate RNAPII processivity and pause sites
Termination Mechanisms
- Transcription termination occurs when RNAPII encounters a terminator sequence in the template DNA
- There are two main termination mechanisms:
- Intrinsic termination: RNAPII releases the transcript due to a pause site or an unstable RNA-DNA hybrid
- Rho-dependent termination: The Rho protein binds to the transcript and stimulates RNAPII release
- RNAPII is released from the template, and the transcript is processed for further maturation
Understand the process of transcription initiation, including the role of RNA polymerase II and general transcription factors. Learn about promoter recognition, elongation, and termination mechanisms.
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