biol139-lecture33-2011

biol139-lecture33-2011 - Gene regulation in prokaryotes...

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Unformatted text preview: Gene regulation in prokaryotes Gene regulation in prokaryotes Chapter 17 Chapter 17 pp 610 - 624 pp 610 - 624 pp 515 - 526 igenetics pp 515 - 526 igenetics BIOL 139 BIOL 139 Operator: Operator: ( lac O ) • between promoter and 1st structural gene but overlaps overlaps promoter • “controlling site” - bind repressor molecule lac Repressor gene lac Repressor gene ( lac I ) • encodes lactose repressor protein and is located upstream from structural genes • own promoter (Pi) and terminator own promoter (Pi) and terminator The The lac lac OPERON OPERON lac repressor protein and negative control Lac Operon is Under Negative Regulation Lac Operon is Under Negative Regulation : : How it works How it works 1. Repression (negative control) 1. Repression (negative control) Repression occurs when Repression occurs when lactose is not present lactose is not present How do we get Induction? Remember Remember : repressor keeps system “off” till induced : repressor keeps system “off” till induced 1. 1. Induction by allolactose Induction by allolactose (derepression) (derepression) Lactose is present!! No glucose Lactose is present!! No glucose Effector Effector Effectors: bind to repressors and change their shape making them non-functional Allosteric shift Mutate inducer-binding domain Mutate inducer-binding domain-will still be able to bind to DNA at-will still be able to bind to DNA at operator, genes will be turned “off” operator, genes will be turned “off”-but non-inducible-but non-inducible called called superrepressor superrepressor (lacI s ) –always off (-/+ lactose) Mutational analysis of the Mutational analysis of the lacI lacI repressor repressor Operator Allolactose Proteins act in Proteins act in trans trans , but DNA sites act only in , but DNA sites act only in cis cis Mutants: Mutants: haploid haploid bacteria bacteria lacI lacI- = repressor mutated repressor mutated in DNA-binding site: always expressed expressed lacI lacI S S = repressor mutated in inducer-binding site: no expression no expression O c c = operator mutated = operator mutated so repressor can’t bind: always expressed expressed Cis-acting elements: DNA Cis-acting elements: DNA • influence the expression of only...
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This note was uploaded on 10/04/2011 for the course BIOL 139 taught by Professor Christinedupont during the Spring '10 term at Waterloo.

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biol139-lecture33-2011 - Gene regulation in prokaryotes...

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