Regulation of Gene Expression

Prokaryotes –Constituitive Gene Expression (promoters) –Regulating Metabolism (promoters and operators) –Regulating Development (sigma switches) Eukaryotes –Regulating genes in multicellular organisms

Constituitive Gene Expression (promoters) promoter coding sequence

Regulating Metabolism (promoters and operators) promoter coding sequence operator

Metabolic signals and repressor activity the regulatory protein is an allosteric protein metabolic signal molecule DNA binding site repressor protein gene off gene ongene off gene on repressor activated repressor deactivated repressor deactivated repressor activated

repressor activated genes OFF repressor deactivated genes ON repressor activated genes OFF repressor deactivated genes ON precursor moleculesmacromolecule energy substrate product Synthetic Pathway Degradative Pathway Repressors & metabolic pathways repression induction

Many regulatory proteins are dimers and bind to palindromes negative controlpositive control

The Tryptophan Operon: Negative control of a synthetic pathway

the lac operon

Negative Control When activated by binding of the metabolic signal molecule, the lac repressor binds to the operator, blocking RNA polymerase

Positive Control cAMP is present when glucose is unavailable cAMP binds to CAP protein, which then binds to the promoter binding of the CAP-cAMP complex to the promoter, activates it

The Lactose Operon: Control of a degredative pathway

Practice

Answers

Control of development: Sigma switching

RNA polymerase in bacteria core enzyme sigma Sigma factors recognize promoters and disassociate when the RNA polymerase binds to the promoter, leaving the core enzyme to make the transcript RNA polymerase

Each sigma can find a certain promoter RNA polymerases

Phage SPOI (in B. subtilis) 3 phases of gene expression –Early phase –Mid phase –Late phase Each phase uses a different sigma, each recognizing a different promoter The genes of each phase all have the same kind of promoter, recognized by one of the sigma factors

Early phase. Early genes have promoters recognized by the host’s RNA polymerase. gp28 is an early protein that acts as a sigma factor for the middle phase genes. gp28 has a higher affinity for the CORE’s binding site than it’s own sigma, thus displacing the host’s sigma and turning off the early genes and turning on the mid genes. Middle phase. Middle phase genes have promoters recognized by gp28. Gp33 and gp34 are middle proteins that act as a sigma factor for the late genes. Late phase early transcripts early proteins, including gp28 host sigma late transcripts late proteins gp33-34 sigma middle transcripts middle proteins, including gp33, gp34 gp28 sigma Sigma Switching

Eukaryotes

Prokaryote versus Eukaryote Comparison Step 1 promoter Step 2 Prokaryotes Step 1 promoter Step 2 Eukaryotes promoter sigma Transcription Factor (eukaryotic sigma)

Positive control in eukaryotes - gene enhancers

Gene activation in Eukaryotes: A different complicated initiation complex for each different context in which a gene is expressed