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Lecture 4

BIO230 Lecture 4.docx

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University of Toronto St. George
Darrel Desveaux

BIO230 Lecture 4 Sept 19, 2013 I suggest you fluff my notes up with someone else's because I don't know how complete they are. Also, the notes only make sense when read along with the slides. If something's on the slides, it probably isn't in my notes. fx = function btw = between Transcription initiation in eukaryotes requires many proteins: general transcription factors these help position RNA polymerase at eukaryotic promoters: contain TATA box required by nearly all promoters used by: RNA polymerase II EUKARYOTIC GENE REGULATION eukaryotic DNA is packaged into chromatin which provides an additional mode of regulation eukaryotic transcriptional requires many gene regulatory proteins - could be thousands in humans all of this added complexity especially in chromatin adds so much complexity when comparing eukaryotes to prokaryotes In eukaryotic transcription, the mediator acts as an intermediary between regulatory proteins and RNA polymerase gene regulatory proteins can be over a thousand base pairs away from the genes they're acting on one mechanism is DNA looping eukaryotic gene regulation proteins often fx as protein complexes on DNA coactivators and corepressors assemble on DNA bound gene regulatory proteins but do not directly bind to DNA activators - activate DNA and bind to DNA co-activators - activate DNA but do not bind to DNA TRANSCRIPTIONAL ACTIVATORS in eukaryotes -have a modular design (have two modules that carry out two separate fxs) 1.modular design: DNA binding domain co activator does not have this 2. activation domain -accelerates the rate of transcription two domains that carry out separate fxs but can be mixed and matched to create chimeric assembly how do activator proteins activate transcription? attract, position and modify: -general transcription factors -mediator -RNA polymerase II they can do this either: 1. directly by acting on these components 2. indirectly modifying chromatin structure (prokaryotes do not have chromatin) DIRECT MECHANISM activator proteins can bind directly to transcriptional machinery or mediator and attract them to promoters INDIRECT MECHANISM involves alteration of chromatin structure activator proteins can alter chromatin structure nucleosomes are the basic structure of eukaryotic chromatin -DNA wound around a histone octamer if you were to unwind our DNA, you have these nucleosomes (beads) every few hundred nucleotides but when they aren't unwound, they look like chromatin fibers. compact. how the fibers actually look, is controversial right now. two options for how they look: 1. zigzag model 2. solenoid model transcriptional machinery cannot assemble when DNA is wound in these compact chromatin fibers so activator proteins ca
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