Class Note for ECOL 320 at UA
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This 9 page Class Notes was uploaded by an elite notetaker on Friday February 6, 2015. The Class Notes belongs to a course at University of Arizona taught by a professor in Fall. Since its upload, it has received 15 views.
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Date Created: 02/06/15
Transcription Control in Eukaryotes Transcription control in eukaryotes is more complex than in prokaryotes With more gene gene interactions presumably required to produce more different cell types in more complex organisms We Will consider some examples and models to illustrate some general principles Example Activation of GAL Genes in Yeast Tightly linked genes GAL1 GAL7 and GAL10 are coordinately activated or repressed by the activity of two genes on different chromosomes Their protein products are enzymes required for conversion of galactose to glucose1phosphate which enters the glycolysis pathway The activator binds to upstream enhancer sequences the indicates that the position of these sites is unknown to me w GAL7 39 GAL10 GAL GAL4 GAL80 General Model of Transcription Control by Activator Proteins and Enhancer Sequences A transcriptional activator protein binds to an enhancer sequence maybe very far upstream or downstream from gene Activator protein binds Transcription Factor IID TATAbinding protein component of TFIID is recruited to the promoter and binds RNA polymerase holoenzyme polymerase plus other proteins RNA polymerase holoenzyme binds to promoter and begins transcription A TFIID Holoenzyme Transcriptional W activator protein Q a H Enhancer Promoter TAT box B C D Text figure 1125 Direction of transcription More Detailed Model of Transcription Initiation Transcriptional activator Transcriptional activator Direction of transcription Promoter region Text figure 1126 Multiple Distant Transcription Control Sites Locus Control Region of the globin genes in the Bglobin cluster lies upstream from Bglobin gene consisting of four different sites There are two more sites downstream which affect gene expression 539 lit1433 I hgpersensitiwe SitES LEE Locus Euntrul Region 39 G 1393 E39HSI H52 H53 H34 E quotf 139 I l I 4m 4 4 E 1 F 4 r E I quotF39 339 DNASE lhnga39Sens 5 i r I3 339H51 39 l 739 prlumnter39 22 J F raginn quot 3 El Gene Regulation by Chromosome Structure DNA duplex 2 nm in quotx 3 39 diameter y DNA in chromosomes is highly folded and compacted partly by being would quot around structures called A nucleosomes made of hlstone jggg g egg 3 g V V llfi mi ii protems i d 9 C 30nm chromatin o v ber BOOum coiled 7 Chromatinfiber o wquot l assoc1ated rotems t v x f p M WM MN M uhy h u w in u w 5 U u x x t u 3 II III 2 7 1 1 1400 nm in diameter Gene Regulation by Chromosome Structure Genes in nucleosomes are inaccessible to transcription complexes Genes must be moved off of nucleosomes before they can be transcribed Text figure 1127 A Inactive conformation TAP binding TBP binding Site Site Nucleosomes B Recruitment of CRC i Chromatinremodeling complex CFICl C Binding sites exposed TAP binding TBP binding Site l Slte TFIID TATAboxbinding protein TBP D Active conformation Transcriptional activator protein TAP Gene Regulation by Chromosome Structure Text figure 710 Chromatin model Sticks are DNA colored spheres are nucleosomes Red spheres labelled A and B are transcription complexes Blue chromatin near B is too dense to allow transcription complex access to genes Yellow chromatin near A is partially unfolded to allow access Coordination 0 Many genes are involved in the transcription control of one gene 0 These genes are controlled by other genes and sometimes by each other 0 Transcription control involves extremely complex networks of gene interactions that must be coordinated 0 Identifying these interactions requires ingenious genetic experiments 0 Understanding the interactions and their coordinations requires highquality mathematical and computer analyses part of the growing field of bioinformatics looking for largescale properties of networks and general rules I zi quotv7quot quot 1 39v A x it as Q a m 4 139 9 xx 39 it r 7 1 remap 15quot Ag q h a quot7 V g n 39 a 39339 j x 2 v a to 7 I 4 7 7
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