Lecture Notes 22

Lecture Notes 22 - Lecture 22 4/3/2008 1 Biosc 0350...

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Unformatted text preview: Lecture 22 4/3/2008 1 Biosc 0350 Genetics Lecture 22 - Eukaryotic gene regulation 1 Prokaryotes ( Lecture 21 ) The lactose operon- Negative regulation by a repressor (lacI)- positive regulation by an activator (CRP) Eukaryotes cis- and trans-acting elements Mechanisms of activation and repression Two examples- tissue specific regulation in Drosophila- Myc/Max system in humans 4/3/08 Martens. Biosc 0350, University of Pittsburgh 2 -galactosidase activity Noninduced Induced wild type No (actually a tiny bit) Yes lacO C Yes Yes ( constitutive ) lacI- Yes Yes ( constitutive ) Both types of mutations prevent repression lacO C defined cis-acting DNA element lacI- defined a trans-acting factor Genetics determined that these two mutations mapped to different chromosomal locations How did they distinguish the mutations in order to come up with the operon model? Lecture 22 4/3/2008 2 4/3/08 Martens. Biosc 0350, University of Pittsburgh 3 Demonstrate cis and trans effects using partial diploids (meroploids) I- Z + Y + I- Z + Y + / I + Z + Y + I + Z + Y + I + Z + Y + I- Z + Y + Construct strains with different lac mutations on either the chromosome or F' lac chromosome F factor F' lac lac lac lac Conjugation: E. coli F (fertility) factor F' is an F factor that contains a few chromosomal genes F' lac plasmid has the lac operon Wild type cells containing F' lac are partial diploids 4/3/08 Martens. Biosc 0350, University of Pittsburgh 4 Function of lacO in partial diploids O c Z + Y- O + Z- Y +-IPTG Conclusions: lacO c on F' has no effect on the lac operon on the chromosome- lacO c is not complemented by lacO + Therefore, lacO (operator) is a cis-acting element (acts on same molecule) Lecture 22 4/3/2008 3 4/3/08 Martens. Biosc 0350, University of Pittsburgh 5 Function of lacI in partial diploids Conclusions: lacI + is dominant to lacI- (or lacI + complements lacI-) Product of lacI, no matter where it is encoded, acts on the lac operon on the chromosome as well as F Therefore, product of lacI is a trans-acting factor that can diffuse within the cytoplasm (Lac repressor) I- Z- I + Z +-IPTG I + Z- I- Z +-IPTG 4/3/08 Martens. Biosc 0350, University of Pittsburgh 6 Another type of lacI mutation lacI s superrepressor can bind DNA, cannot bind inducer non-inducible - galactosidase activity Noninduced Induced lacI + No Yes lacI S No No Lecture 22...
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This note was uploaded on 04/07/2008 for the course BIOSC 0350 taught by Professor Josephmartens during the Spring '08 term at Pittsburgh.

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Lecture Notes 22 - Lecture 22 4/3/2008 1 Biosc 0350...

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