Regulation of Gene Expression In Prokaryotes. Regulation of Gene Expression Constituitive Gene...
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Regulation of Gene ExpressionIn Prokaryotes
Regulation of Gene Expression
• Constituitive Gene Expression (promoters)
• Regulating Metabolism (promoters and operators)
• Regulating Development (sigma switches)
Constituitive Gene Expression (promoters)
promoter coding sequence
Regulating Metabolism (promoters and operators)
promoter coding sequenceoperator
Major and minor grooves - protein binding
Major and minor grooves - protein binding
Recognition involves the major groove
Regulatory Proteins Bind DNA
Many regulatory proteins are dimers and bind to palindromes
negative control positive control
repressor activatedgenes OFF
repressor deactivatedgenes ON
repressor activatedgenes OFF
repressor deactivatedgenes ON
precursor molecules macromolecule
energy
energy
substrate
product
Synthetic Pathway
Degredative Pathway
Repressors & metabolic pathways
Metabolic signals and repressor activity
metabolic signal
molecule
DNAbinding
site
repressorprotein
gene off
gene ongene off
gene on
the lac operon
Lactose Metabolism
the metabolic signal for repression
Negative ControlWhen activated by binding of the metabolic signal molecule,
the lac repressor binds to the operator, blocking RNA polymerase
Negative control in the lac operon
the lac operon
Conventional interpretation of dominance - focusing on enzyme function
QuickTime™ and aAnimation decompressor
are needed to see this picture.
Conventional interpretation of codominance - focusing on enzyme function
QuickTime™ and aAnimation decompressor
are needed to see this picture.
But alternatively, control regions can be involved - a recessive operator mutation
But alternatively, control regions can be involved - a dominant operator mutation
But alternatively, control regions can be involved - one inducer mutation
But alternatively, control regions can be involved - another inducer mutation
the Lac control region
Cyclic AMP
Positive ControlcAMP is present when glucose is unavailable
cAMP binds to CAP protein, which then binds to the promoterbinding of the CAP-cAMP complex to the promoter, activates it
CAP-cAMP positioning of CTD
CAP-cAMP acts in formation of closed promoter
The Lactose Operon:Control of a degredative pathway
Practice
Answers
Trp operon, control of aa biosynthetic pathway
The Tryptophan Operon:Control of a synthetic pathway
TryptophanSynthesis
allosteric
protein
Attenuation of trp
The leader sequence:two trp codons and a stop codon
The mechanism of attenuation - termination
Region 2 can bind with 1 or 3, but affinity for 1 is higher
Over riding attentuation if shortage of trp causes ribosome to stall, 2 binds with 3
…no terminator hairpin forms
Control of development:Sigma switching
Different sigmas and their regions of homology
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
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 gp28host
sigma
late transcripts
late proteinsgp33-34 sigma
middle transcripts
middle proteins,including gp33, gp34gp28
sigma
Sigma Switching
Lambda
Lysogenic Life Cycles - Temperate Viruses
Genetic map of Lambda
3 phases again
N antitermination
Q antitermination
cI and cro duke it out
Establishing Lysogeny
Maintaining Lysogeny
InductionSOS
Prokaryote versus Eukaryote Comparison
Step 1
promoter
Step 2
Prokaryotes
Step 1
promoter
Step 2
Eukaryotes
promotersigma
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