U01.01.011 Regulation of gene expression

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Learning Objectives

  • Identify the Promoter as the primary site for transcription initiation.
  • Contrast the functions of Enhancers (activation) and Silencers (repression).
  • Explain the clinical impact of Promoter mutations on gene transcription levels.
  • Define Epigenetics and the three primary mechanisms of non-sequence-based inheritance.

1. The Promoter: The Initiation Site

The promoter is a specific DNA sequence located upstream from the gene locus. It serves as the landing pad for RNA Polymerase II and essential transcription factors.

  • Key Sequences: Typically AT-rich to allow for easier strand separation. Common elements include the TATA box and the CAAT box.
  • Clinical High-Yield: A mutation in the promoter typically leads to a dramatic decrease in transcription, as the “start signal” is effectively broken.

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2. Distant Regulation: Enhancers & Silencers

Unlike promoters, these regulatory elements are position-independent. They can be located near the gene, thousands of base pairs away, or even hidden within an intron.

Element Binding Protein Effect on Expression
Enhancer Activators Increases gene expression.
Silencer Repressors Decreases gene expression.

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3. Epigenetics: Inheritance Beyond the Sequence

Epigenetics refers to heritable changes in gene expression that do not alter the underlying DNA sequence. These changes can be passed down through both mitosis and meiosis.

  • DNA Methylation: Often silences genes (CpG islands).
  • Histone Modification: Acetylation (activates) vs. Deacetylation (silences).
  • Noncoding RNA: MicroRNAs (miRNAs) and others that regulate translation or stability.

 

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