Regulation of transcription in eukaryotes

Regulation of transcription is usually complex in eukaryotes

Example: Activation of transcription by Gal4 in yeast

Reporter genes can be used to study transcription factors and their binding sites

Eukaryotic transcription activators have DNA binding domains similar to their bacterial counterparts Homeodomain Zinc finger domain Helix-loop-helix Leucine zipper

Multiple targets of an activator

Activation of transcription by tethering the mediator to the DNA

Activator-induced chromatin and nucleosome remodeling (similarly a repressor can induce changes in chromatin)

Elongation factors help RNA polymerase to overcome a stall

Insulators restrict enhancer function to specific regions

Some gene clusters are regulated by locus control regions

Cooperative binding of transcription factors

Control of HO gene expression in budding of yeast Recruits nucleosome modifiers Recruits mediator

The ß-interferon enhanceosome Activated upon viral infection Architectural protein Chromatin and nucleosome modifiers

Structure of the ß-interferon enhanceosome

Combinatorial control of gene expression

Combinatorial control of mating type gene expression in yeast

Mechanisms of gene repression in eukaryotes

Gal1 gene repression by Mig1

Signal transduction pathways and control of transcription factors in mammals

Indirect unmasking of the Gal4 activating region by galactose

Heterochromatin DNA is not accessible for transcription DAPI staining of heterochromatin in Arabidopsis

Heterochromatin DNA is not accessible for transcription

Heterochromatin formation is done by recruitment of chromatin modifying complexes. Those complexes are recruited by histone modification or DNA methylation.

Formation of heterochromatin at telomeres in yeast Histone methylation

Positional effect of gene expression Location in heterochromatin Position variegation in Drosophila Histone methylation

Repression by Polycomb PRC: polycomb repressive complex PRE: polycomb response element Histone methylation

Gene silencing by DNA methylation

Maintenance and de novo DNA methylation

Methylation of upstream sequences silences downstream genes

Imprinting is mediated by DNA methylation

Epigenetic regulation of gene expression Self-maintained repression of gene expression in bacteriophage lambda

Epigenetic maintenance methylation in vertebrates

De novo methylation is required for development