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Chapter 17
Regulation in Eukaryotes
1 and 3 November, 2006
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Overview
Transcriptional initiation is the most common point to regulate gene expression.
Eukaryotes must also integrate more signals, and must modify nucleosome
positioning in order to activate transcription.
Eukaryotic transcriptional activators are often modular, with DNA binding and
activation domains.
Eukaryotic transcriptional activators may bind as heterodimers.
Classes of eukaryotic transcriptional activators include homeodomain, zinc finger,
leucine zipper, and helix-loop-helix.
Activators recruit the transcriptional machinery to the gene, interacting with
mediator or TFII general factors.
Activators may also promote chromatin modification.
Insulators block activation by enhancers.
Locus control regions open up chromatin to regulation by activators.
Activators act synergistically.
Eukaryotic transcription may be repressed by blocking or binding activators,
interacting with mediator, or by modifying chromatin.
Signal transduction pathways communicate with transcriptional regulators.
DNA and histone modification can collaborate to effect regulation.
Regulation may also occur at the levels of splicing, translation, and RNA stability.
Complex Eukaryotic Regulatory Regions
Modular Transcriptional Activators
The Two-hybrid System Again!
Homeodomain
Zinc Finger
Leucine Zipper
Helix-Loop-Helix
Potential Activator Contacts
Activator Bypass by LexA-Mediator Fusion
ChIP can
identify
binding sites.
Binding and Recruitment Assay
Gal4 recruits TFIIB
Activators may promote histone acetylation
and / or chromatin remodeling.
Insulators block the effects of activators at enhancers.
Locus control regions make clusters of genes
available for activation.
Possible
Modes of
Cooperative
Binding of
Activators
Synergistic Action of SWI5 and SBF in HO
Expression
Signal integration at the INF-b gene
Combinatorial Control
Control of Cell-type Specific Genes in Yeast
Possible
Modes of
Action for
Eukaryotic
Repressors.
Signal
transduction
pathways
regulate
transcription
factors.
Gal80 Regulates Gal4
Silencing through Histone Deacetylation
Silencing sometimes involves methylation and
histone deacetylation.
Imprinting
Methylation patterns are heritable.
Transcriptional Regulation of Sxl
Regulated
Alternative
Splicing
Translational
Control of
GCN4
RNAi
Cooperative and Non-Cooperative Binding
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