3.22.07 - 3.22.07 Estrogen o Positive and inducible o...

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3.22.07 Estrogen: o Positive and inducible o Positive because presence of the estrogen receptor increases transcription and when estrogen is abundant it increases expression Protein Organism DNA Sequence it binds Effect Activator Eukaryotes Enhancer (ERE is an example of an enhancer) ERE is located far away from the gene that it controls, it could be 1000 nucleotides up/down stream of the gene, it can function so far away because it causes DNA to flip over and bring DNA in contact with the transcription factors and promoter. Enhancer is cis acting because its effect is for genes on the same DNA molecule (just far away) – distant cis acting element. Increase transcription Activator Prokaryotes Promoter CAP is an example of one, don’t have distantly acting cis elements in prokaryotes so where does an activator bind? promoter Increase transcription Repressor Eukaryotes Silencer Don’t really have operators; repressors can bind to sequences called silencers. Silencer like an enhancer is a distantly acting cis element. Silencer can be positioned right next to an enhancer so when a repressor binds to a silencer it blocks an enhancer. Or repressor can bind to silencer and flips DNA and causes an interaction between the silencer and transcription site to block complexes from coming together. Decrease Transcription Repressor Prokaryotes Operator Decrease Transcription o Don’t need to know the names of the categories for all the small molecules, only one we’ve mentioned is that alolactose is an inducer (removes a repressor from an inducible gene) GAL system – in yeast – breaks down galactose o (Response element) (Promoter)(GEANTCgal) GAL4 binds to response element, activator, has two binding sites (one is a DNA binding domain specific for this response element) other is a protein binding site for GAL80 which is just another regulatory protein GAL4 can’t act like most activators with GAL80 sitting on it This happens when galactose is absent, which makes sense because if this carbon source isn’t here then why would yeast need the enzyme to break it down When galactose is present GAL80 also has two binding sites, one is a protein binding site for GAL4 the other is a binding site for galactose GAL80 bound to galactose has a slightly different shape than GAL80 not bound to galactose, when GAL80 is bound to galactose it is not in the right shape to bind to GAL4 and it lets go of it so that GAL4 can do what its supposed to do GAL4 will flip the DNA around so that it is positioned above the promoter to bind to transcription factors bound to the promoter to stabilize them and keep them there long enough for the transcription complex to initiate transcription So if galactose is present the cell will be able to break it down o What is the regulatory protein that binds DNA?
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