Explain the role of transcription factors of RNA polymerase II in eukaryotes. (IFS 2019, 10 Marks)

Introduction

Transcription factors are essential proteins that play a crucial role in the regulation of gene expression in eukaryotes. RNA polymerase II is the enzyme responsible for transcribing protein-coding genes into messenger RNA (mRNA) in eukaryotic cells. Transcription factors interact with RNA polymerase II to ensure that the correct genes are transcribed at the right time and in the right amount.

Role of Transcription Factors of RNA Polymerase II in Eukaryotes

1. General Transcription Factors (GTFs):

• GTFs are a set of proteins required for the initiation of transcription by RNA polymerase II.
• They help in the binding of RNA polymerase II to the promoter region of the gene, as well as in the formation of the transcription pre-initiation complex (PIC).
• Key GTFs:
  
  • TFIID: Composed of the TATA-binding protein (TBP) and TBP-associated factors (TAFs), it binds to the TATA box in the promoter.
  • TFIIB: Helps in positioning RNA polymerase II correctly at the promoter.
  • TFIIE: Facilitates the recruitment of other factors and ensures the stability of the pre-initiation complex.
  • TFIIH: Contains helicase activity to unwind DNA, allowing for the formation of an open transcription bubble.

2. Specific Transcription Factors:

• These are regulatory proteins that bind to specific DNA sequences in gene promoters or enhancers, influencing transcription rates.
• They modulate the transcription of specific genes in response to environmental signals or cellular needs.
• Activators: These transcription factors increase the rate of transcription. They bind to enhancer sequences and recruit coactivators, which help RNA polymerase II function more efficiently.
• Repressors: These transcription factors decrease the transcription of specific genes by binding to silencer sequences and inhibiting RNA polymerase II activity.

3. Coactivators and Corepresors:

• Coactivators: These are non-DNA binding proteins that interact with activators and RNA polymerase II to enhance transcription. Examples include the Mediator complex, which helps in the formation of the transcription complex.
• Corepressors: Proteins that do not bind DNA directly but interact with repressors to suppress transcription. They typically function by modifying chromatin structure or recruiting histone deacetylases.

4. Role in Gene Expression Regulaton:

• Transcription factors regulate gene expression by interacting with RNA polymerase II and influencing the transcriptional rate of specific genes.
• These factors are responsible for temporal and tissue-specific expression of genes, ensuring proper development and response to stimuli.
• In addition to activating or repressing transcription, transcription factors can also play a role in the process of RNA splicing, stability, and post-transcriptional modification.

5. Post-translational Modifications of Transcription Factors

• Transcription factors are often regulated by post-translational modifications (e.g., phosphorylation, acetylation, ubiquitination).
• These modifications can alter their activity, localization, or ability to bind to DNA, thereby modulating transcription in response to cellular conditions.

6. Role in Disease

• Mutations or dysregulation of transcription factors can lead to various diseases, including cancer, developmental disorders, and neurodegenerative diseases.
• Overexpression of specific transcription factors may lead to uncontrolled cell division, while the loss of others can impair normal cellular function.

Conclusion

Transcription factors of RNA polymerase II play a critical role in the regulation of gene expression in eukaryotes. By interacting with RNA polymerase II, promoters, enhancers, and the mediator complex, transcription factors ensure that genes are transcribed accurately and in response to various cellular signals.