f2 - Eukaryotic Gene Regulation Eukaryotic Gene Regulation...

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Eukaryotic Gene Regulation Ch11: pp 447-491 Ch12: pp 518-529 Eukaryotic Gene Regulation transcriptional level post-transcriptional level
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Where can eukaryotic gene expression be controlled? • There are many points along the pathway from DNA Protein where the process can be regulated… -turned on or off -sped up or slowed down
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Eukaryotic Regulatory Elements • Regulatory elements can be located near the promoter or from a long distance –Promoter-proximal element (PE): located within 100 – 200 bp upstream of the start site; can be cell-type specific Enhancers (green): can stimulate transcription from up to 50 kb from the start site Can be located upstream or downstream from the start site, even within an intron Are often cell-type specific Can increase transcription up to 1,000X
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Transcription Activators and Repressors: Structure (Review p 461-468) • In both prokaryotes and eukaryotes, transcriptional activators and repressors are modular proteins , composed of distinct functional domains …can function without the other –DNA binding domain: binds DNA; usually one domain –Activation/repression domain: interacts with other proteins or another subunit of the same protein; 1 can be present
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Heterodimerization expands the diversity of regulatory factors that can be generated 3 bHLH proteins can make 6 different transcription factors Many transcription factors function as dimers
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Possible Mechanisms of Transcriptional Activation • Recruit transcription factors to vicinity of promoter (increase the local concentration) • Stabilize formation of pre-initiation complex • Disrupt local chromatin structure • Acetylation/deacetylation of histones
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Transcriptional Activators • Bind to specific DNA sequences • Stimulate transcription • Two domains (regions) are critical –DNA binding domain –activation domain
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How do enhancers stimulate transcription from a distance? • Enhancers are composed of one or more binding sites for regulatory proteins, such as activators and repressors • Activators interact with other proteins (i.e. mediator complex) to bring in and stabilize transcription machinery, causing the intervening DNA to loop out • Mediator is the molecular bridge between activators and RNA Pol II
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• Several DNA-bound activators can interact with a single mediator complex • The mediator complex is a type of co-activator—intermediary proteins that assist the transcription activators to stimulate initiation of transcription • Subunits of a mediator can bind to RNA pol II, activation domain of various activator proteins, and histone acetylation activity How do enhancers stimulate transcription from a distance?
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Comparison of prokaryotic and eukaryotic activation Eukaryotes : activator interacts with many proteins to recruit general transcription factors and RNA pol from a distance, leading to a loop in the DNA Prokaryotes : activator binds immediately upstream of polymerase and directly contacts polymerase
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If the expression of each
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