Goals: Discuss 3 examples of transcriptional regulation
-Lac operon
-Coordinated gene regulation
-Regulation of transcription without regulation of polymerase
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
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)
The activator and repressor are both inhibited by sugars
Physical interactions regulate lac operon transcription
Cap recruits Polymerase via interaction with the CTD of the alpha subunit
The cap activator is a helix-turn-helix motif
-Bind DNA as a dimer
-Requires two similar sequences of DNA in reverse order
Lac repressor forms a tetramer between two operator sites (primary and secondary)
Discovery of the cis-trans model of gene regulation
Repressor acting in trans
Operator (repressor binding site) operates in cis
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
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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