341lecture14oct12sakai

341lecture14oct12sakai - Cell Biology 341 Last lecture:...

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Cell Biology 341 Monday, October 12, 2009 Today: How do eucaryotic activators increase the level of transcription? Examples of eucaryotic promoters and activators Last lecture: Negative regulation: the trp repressor binds Trp → binds operator DNA → blocks RNA pol binding procaryotic activators such as cAMP- CAP increase the rate of RNA pol binding DNA-binding proteins use multiple noncovalent binding interactions to bind a specific DNA sequence Examples of DNA-binding motifs: helix- turn-helix (found in homeodomain activators), zinc finger, β sheet, leucine zipper and helix-loop-helix proteins
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Leucine zippers and helix-loop-helix proteins grip DNA like a pair of tongs Figure 7-19, 7-23 two amphipathic helices these proteins are obligate dimers Both types of proteins use two α helices, one from each subunit, to bind a specific DNA sequence in the major groove The dimerization domain of a leucine zipper is a coiled coil stabilized by hydrophobic interactions Hydrophobic amino acids such as leucine occur every seven amino acids in the upper helices of a leucine zipper The lower helices of both leucine zippers and helix-loop- helix proteins are rich in basic lysine and arginine residues
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341lecture14oct12sakai - Cell Biology 341 Last lecture:...

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