Lecture.14.Fall.2013

Core promoter the site where rnp ii binds to dna and

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Unformatted text preview: oter regions • Much more highly regulated – Enhancer sequences Eukaryotic Promoters are Complex I count 24 proteins bound to at least six sites on the DNA And this doesn’t even include distant enhancer elements Eukaryotic Promoters Are Complex • Three well-studied types of cis-acting sequences: 1. Core promoter: the site where RNP II binds to DNA and initiates transcription: – TATA box, located at -30 (TATAAAA) found in both euc and bac. – CAAT box (GGCCAATCT), within 100 bp of the start site (upstream) – Initiator element (contains transcriptional start site) Eukaryotic Promoters Are Complex 2. Regulatory promoter: directly upstream of the core promoter •A variety of protein-binding sequences •In mix-and-match combinations •Regulates the rate of transcriptional initiation (promoter “strength”) Enhancers 3. Enhancer elements • Can be found anywhere within or near a gene, or even thousands of base pairs from the start site • Can function in either orientation (can be flipped 5’-to-3’ and will still regulate transcription • Enable much more complicated gene regulation (more on this later) • Some enhancers are tissue- or cell type-specific • Others are active only at specific developmental times • Still others respond to particular environmental conditions Enhancers Very generic mode of action: transcription factors bind to the enhancer, bend the DNA, and bring the start site closer to the regulatory regions Transcription Factors • Promoters and enhancers are the cis-elements bound by trans-acting “transcription factors” • Transcription factor = any protein that is required to initiate, enhance, or repress transcription • Two types: – General transcription factors: all transcription (TFIIA, TFIIB, TFIID, etc.) – Specific transcription factors: bind to enhancer elements and regulate the particular expression of a gene Eukaryotic Transcription: How it differs • Chromatin must be remodeled to allow transcription factors access to th...
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