Chapter 7: Operons & Control of Prokaryotic Transcription Flashcards
activator protein
stimulates transcription (allolactose)
ara operon
catabolic, repressible
contains 2 operators, control gene, CAP-binding site (200bp upsteam of promoter)
4 arabinose-metabolizing genes (A-D) and AraC gene
regulated by AraC protein & DNA looping
turns operon (switch) off
Repressor
cluster of genes containing an operator, promoter, and metabolic enzyme genes
Operon
main operator (O1 @ +11) and 2 auxillary operators (O2 @ +412 & O3 @ -82)
3 lac operators
inducer in lac operon
produced by B-gal from lactose
allolactase
Muller-Hill
performed genetic mutations in each of the 3 (E. coli) lac operators and found they repressed lacZ transcription ~1300-fold
single mRNA from >1 gene (i.e. lac genes)
polycistronic message
3 enzymes needed to metabolize lactose (by E. coli)
galctoside permease (lacY), B-galactosidase (lacZ), and galactoside transacetylase (lacA)
araO2
250bp upstream of promoter
controls transcription b/c DNA loops out from protein-DNA & protein-protein interactions (prevents RNA polymerase binding promoter)
Repressor
turns operon (switch) off
AraC
exerts negative control w/ out arabinose, positive control w/ arabinose (binds O1, O2, l1, and l2 within operator)
also engages in autoregulation, binding O1 (controls leftward transcription of araC) and inhibiting its own production when araC levels are high
attenuation
used in negative control of trp operon
trp leader & attenuator DNA (aka attenuator; between operator and first trp E gene) form inverted repeat (3&4) in RNA (hairpin), stopping translation through ribosome (and possibly RNA polymerase) interferance
blocked by low trp levels (2-3 pairing prevents 3-4 and creates strong ribosome-binding site)
galctoside permease (lacY), B-galactosidase (lacZ), and galactoside transacetylase (lacA)
3 enzymes needed to metabolize lactose (by E. coli)
3 lac operators
main operator (O1 @ +11) and 2 auxillary operators (O2 @ +412 & O3 @ -82)
contacts DNA & CTD of holoenzyme, causing closed promoter complex formation and transcription initiation (when bound to cAMP; independent of allolactose)
CAP (catabolite activator protein)
performed genetic mutations in each of the 3 (E. coli) lac operators and found they repressed lacZ transcription ~1300-fold
Muller-Hill
Operon
cluster of genes containing an operator, promoter, and metabolic enzyme genes
stimulates transcription (allolactose)
activator protein
negative control
always on unless something stops it (lac operon)
binds operator to prevent RNA polymerase transcription
allosterically regulated w/ inducer (allolactase) binding
lac repressor
allolactase
inducer in lac operon
produced by B-gal from lactose
exerts negative control w/ out arabinose, positive control w/ arabinose (binds O1, O2, l1, and l2 within operator)
also engages in autoregulation, binding O1 (controls leftward transcription of araC) and inhibiting its own production when araC levels are high
AraC
cAMP
second messenger derived from ATP (using adenylyl cyclase) sensitiveto low glucose levels
stimulates lac operon with catabolite activator protein (CAP) association by binding activator site containing TGTGA (facilitates RNA polymerase binding to promoter and opens up DNA)
polycistronic message
single mRNA from >1 gene (i.e. lac genes)
used in negative control of trp operon
trp leader & attenuator DNA (aka attenuator; between operator and first trp E gene) form inverted repeat (3&4) in RNA (hairpin), stopping translation through ribosome (and possibly RNA polymerase) interferance
blocked by low trp levels (2-3 pairing prevents 3-4 and creates strong ribosome-binding site)
attenuation
always on unless something stops it (lac operon)
negative control
catabolic, repressible
contains 2 operators, control gene, CAP-binding site (200bp upsteam of promoter)
4 arabinose-metabolizing genes (A-D) and AraC gene
regulated by AraC protein & DNA looping
ara operon
developed the E. coli lac operon
Francois Jacob & Jacques Monod (1940’s)
CAP (catabolite activator protein)
contacts DNA & CTD of holoenzyme, causing closed promoter complex formation and transcription initiation (when bound to cAMP; independent of allolactose)
anabolic, repressible
contains 5 genes & operator w/in promoter
trp operon
trp operon
anabolic, repressible
contains 5 genes & operator w/in promoter
250bp upstream of promoter
controls transcription b/c DNA loops out from protein-DNA & protein-protein interactions (prevents RNA polymerase binding promoter)
araO2
lac repressor
binds operator to prevent RNA polymerase transcription
allosterically regulated w/ inducer (allolactase) binding
Francois Jacob & Jacques Monod (1940’s)
developed the E. coli lac operon
second messenger derived from ATP (using adenylyl cyclase) sensitiveto low glucose levels
stimulates lac operon with catabolite activator protein (CAP) association by binding activator site containing TGTGA (facilitates RNA polymerase binding to promoter and opens up DNA)
cAMP
