Goals: Discuss 3 examples of transcriptional regulation Lac operon Coordinated gene regulation
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Goals: Discuss 3 examples of transcriptional regulation
-Lac operon
-Coordinated gene regulation
-Regulation of transcription without regulation of polymerase
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Gene expression can be regulated at any point between transcription and translation
-Binding of pol II to the promoter
-Melting
-Release from promoter/elongation
-During elongation
-RNAi - destroys mRNA
-During translation
-After translation
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The lac operon promoter
LacZ - BetaGalactosidase - cleaves lactose into usable subunits
LacY - Lactose permease - transports lactose across the cell membrane
LacA - Eliminates toxic molecules that are co-transported
Operator - Binds repressors
CAP site - binds cap proteins (activator)
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The activator and repressor are both inhibited by sugars
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Physical interactions regulate lac operon transcription
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Cap recruits Polymerase via interaction with the CTD of the alpha subunit
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The cap activator is a helix-turn-helix motif
-Bind DNA as a dimer
-Requires two similar sequences of DNA in reverse order
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Lac repressor forms a tetramer between two operator sites (primary and secondary)
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Discovery of the cis-trans model of gene regulation
Repressor acting in trans
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Operator (repressor binding site) operates in cis
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Use of different sigma proteins to regulate gene expression
-Bacterial phage SPO1 uses host RNA polymerase to transcribe its genes
-Early genes use sigma 70, encode an alternative sigma
-Alternative sigma out competes sigma 70, binds to different promoter architecture
-Second set of genes are driven by new sigma protein
-Process repeats until all genes are expressed, in correct order for phage release
Sets of genes are coordinated by using similar promoters
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Regulation of transcription without interaction with RNA polymerase
-Mercury resistance genes = merT
-MerR is activator, binds between -10 and -35 promoter elements
-Promoter elements are not optimally aligned
-MerR, in the presence of mercury, contorts DNA such that promoter elements are optimally alligned
-Activator doesn’t interact with Polymerase
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