state that transcription factors are proteins that bind to DNA and are involved in the control of gene expression in eukaryotes by decreasing or increasing the rate of transcription

Published by Patrick Mutisya · 14 days ago

Gene Control – Transcription Factors

Gene Control

Learning Objective

State that transcription factors are proteins that bind to DNA and are involved in the control of gene expression in eukaryotes by decreasing or increasing the rate of transcription.

Key Concepts

  • Transcription factors (TFs) are regulatory proteins.

  • They bind to specific DNA sequences called cis‑regulatory elements (e.g., promoters, enhancers, silencers).

  • Binding can either activate (increase) or repress (decrease) transcription of the associated gene.

  • TFs work in concert with RNA polymerase II and other co‑activators or co‑repressors.

How Transcription Factors Influence Transcription

  1. DNA Binding: TFs contain DNA‑binding domains (e.g., zinc finger, helix‑turn‑helix, leucine zipper) that recognise specific nucleotide motifs.

  2. Recruitment of the Transcriptional Machinery: Activator TFs attract RNA polymerase II and general transcription factors to the promoter, forming the pre‑initiation complex.

  3. Chromatin Remodeling: Some TFs recruit chromatin‑remodelling complexes that modify histones, making DNA more accessible.

  4. Repression: Repressor TFs can block the binding site for activators or recruit co‑repressors that tighten chromatin structure.

Typical Structure of a Transcription Factor

DomainFunction
DNA‑binding domainRecognises and binds specific DNA sequences.
Activation/repression domainInteracts with other proteins to modulate transcription.
Regulatory domainResponds to cellular signals (e.g., phosphorylation, ligand binding).

Examples of Transcription Factors in Eukaryotes

  • Sp1 – binds GC‑rich promoter regions and activates transcription.

  • p53 – can act as an activator of genes involved in cell‑cycle arrest or apoptosis, and also represses certain genes.

  • NF‑κB – activated by signalling pathways; promotes transcription of immune‑response genes.

  • Oct‑4 – maintains pluripotency in embryonic stem cells.

Regulatory Scenarios

Consider a gene with an enhancer element located 1 kb upstream of the transcription start site. An activator TF binding to this enhancer can increase the transcription rate by up to 10‑fold, whereas a repressor TF binding to a silencer element downstream of the gene can reduce transcription to 5 % of the basal level.

Suggested diagram: A schematic showing an activator TF bound to an enhancer, recruitment of RNA polymerase II, and a repressor TF bound to a silencer inhibiting transcription.

Summary

Transcription factors are essential proteins that bind to specific DNA sequences and modulate the rate of transcription in eukaryotic cells. By acting as activators or repressors, they provide a flexible mechanism for cells to respond to internal and external cues, ensuring appropriate gene expression patterns.