LIFESCI 4 Lecture Notes - Lecture 13: Lac Repressor, Lac Operon, Repressor
Transcriptional regulation
• Tool: F’ fator
- F’ fator = La in F fator
Lactose metabolism
• Lac Z encodes Beta-Gal
• Lac I encodes Lac repressor, is not part of Lac Operon, has its own promoter
• Lac P is Lac Operon promoter (promoter region for Z, Y, A genes); RNA pol binds
• O is operator: repressor binding site located in promoter region -> prevents RNA pol.
from binding promoter/moving forward
- If something binds to operator, NO transcription
• Lac I is a regulatory region where inducer interacts with
• Lac repressor constitutively synthesized in another promoter other than Beta-Gal, and is
ALWAYS ON -> repressor always bound to operator
- Lac repressor binds on operator site of promoter that controls Beta-Gal expression
- Can come on/off the operator based on if it’s ound to latose
• When allolactose binds repressor -> change shape -> Lac repressor comes off of
operator -> can transcribe low level of beta-Gal & transporter
• Low level transcription occurs when both sugars present
- Hae gluose, don’t really need beta-Gal
- But also have lactose, and repressor came off
• To get high level, need activator
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Document Summary
F" fa(cid:272)tor = la(cid:272) in f fa(cid:272)tor. If something binds to operator, no transcription: lac i is a regulatory region where inducer interacts with, lac repressor constitutively synthesized in another promoter other than beta-gal, and is. Always on -> repressor always bound to operator. Can come on/off the operator based on if it"s (cid:271)ound to la(cid:272)tose. But also have lactose, and repressor came off: to get high level, need activator. Need to not only remove negative regulation of lac operon, also need positive regulation for high level: activator binding site upstream to promoter. Positive regulation on when no glucose present. Iptg can bind to lac repressor -> induce lac operon. So when added, will cause induction, but has constant concentration: lactose as inducer: beta-gal concentration levels off with time (lactose cleaved over time & repressor binds operator again) Iptg as inducer: beta-gal concentration increases steadily (iptg not cleaved) Oc = (cid:272)onstituti(cid:448)e; doesn"t allo(cid:449) repressor to (cid:271)ind.
