Mediator complex

Definition

The mediator complex is a multi-subunit protein complex that serves as a crucial intermediary between gene-specific transcription factors and the RNA polymerase II enzyme during transcription initiation in eukaryotic cells. This complex is essential for the regulation of gene expression, as it facilitates the assembly of the transcription machinery at the promoter region of genes, thereby influencing the transcription process.

5 Must Know Facts For Your Next Test

1. The mediator complex consists of over 30 different subunits, allowing it to interact with various transcription factors and RNA polymerase II.
2. One of the key functions of the mediator complex is to bridge the gap between enhancers (which are distant regulatory sequences) and the core promoter, facilitating long-range regulatory interactions.
3. The mediator complex plays a role in both activating and repressing transcription, depending on the context of its interactions with different transcription factors.
4. Mutations or alterations in components of the mediator complex can lead to various diseases, including cancer, due to disrupted gene expression regulation.
5. The mediator complex is not directly involved in catalyzing the formation of RNA; instead, it acts as a scaffold that brings together necessary components for efficient transcription initiation.

Review Questions

• How does the mediator complex facilitate the interaction between transcription factors and RNA polymerase II during transcription initiation?
  • The mediator complex acts as an intermediary by binding to both gene-specific transcription factors and RNA polymerase II. When transcription factors recognize and bind to specific DNA sequences near a gene's promoter, they recruit the mediator complex. This complex then interacts with RNA polymerase II, helping to assemble the entire transcription machinery at the core promoter, ensuring that transcription can be initiated effectively.
• What role does the mediator complex play in regulating gene expression, and how can its dysfunction contribute to diseases?
  • The mediator complex regulates gene expression by influencing the recruitment of RNA polymerase II and modulating the activity of various transcription factors. Its ability to act as a bridge between enhancers and promoters allows for precise control over which genes are expressed under specific conditions. When components of the mediator complex are dysfunctional due to mutations or alterations, this can lead to improper regulation of genes, contributing to diseases such as cancer by allowing unchecked cell growth or other aberrant behaviors.
• Evaluate the importance of the mediator complex in eukaryotic transcription compared to prokaryotic systems, focusing on its structural and functional differences.
  • The mediator complex is vital for eukaryotic transcription because it coordinates multiple regulatory inputs at a gene's promoter, which is a feature not seen in prokaryotic systems. In prokaryotes, transcription initiation is relatively simpler, often requiring only RNA polymerase and a few general transcription factors without a mediator-like structure. The complexity and versatility provided by the mediator complex in eukaryotes allow for sophisticated regulation of gene expression in response to various internal and external signals, making it essential for processes like development, differentiation, and response to environmental changes.

Related terms

RNA polymerase II: An enzyme responsible for synthesizing mRNA from a DNA template during transcription in eukaryotic cells.

Transcription factors: Proteins that bind to specific DNA sequences and regulate the transcription of nearby genes by enhancing or inhibiting the recruitment of RNA polymerase.

Core promoter: The region of DNA located immediately upstream of a gene, where RNA polymerase II and general transcription factors assemble to initiate transcription.