CMMB 403 Lecture Notes - Lecture 5: Globin, Demethylation, Chromatin
20 Sep 2018
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An enhancer is a non coding (doesn"t produce mrna) dna sequence that binds transcription factors and activates transcription of a specific gene in cis1. Separate, discrete enhancers often control the expression of a developmental gene in different tissues. Enhancers are often tissue-specific, meaning that they can activate gene transcription in one tissue. Mutations in an enhancer can cause a very-tissue specific phenotype. There are often 1 or more tissue specific enhancers working on a gene. Example: shh (sonic hedgehog gene) picture on right. Coloured rectangles are enhancers, and they control expression in different parts of the endoderm. Blue enhancer controls shh expression in mouth region. Red enhancer controls shh expression in pharynx region. Green enhancer controls shh expression in major organs. The role of the mediator complex in forming the transcription pre-initiation. Relatively open chromatin is composed of dna coiled around nucleosomes. Transcription factors bind to the enhancer and to nucleosome-modifying enzymes that remove nucleosomes from the area.
