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Lecture 19

Lecture 19 - Repair&Operon - BIOL308.pdf

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BIOL 308
Bruce Wolff

Lecture 19Repair of constitutive mutation lac IComplementation in actionGenomic DNAlacI mutation produced repressor cannot bind to operatorConstitutive mutation normal beta gal always sunthesizeBut plasmid carries normal lacIPlasmid carries mutated Z genePlasmids lacIgene codes for a diffusible elementthat acts in trans by binding toany operatorit encounters regardless of chromosomal locationSynthesis of normal beta gal will become regulatedCoded by genomic DNAWhat is actually happening step by stepStep by stepLac absentLac presentsNoninducible mutation lac IslacI superrepressor lacImutant carried by plasmidcan not bind inducer lactoseAll operator sites O eventually occupied by superrepressorBeta gal normal coded by chromosome will stop being producedslacImutant encodes a diffusible element that acts in trans by binding to any operatorit encountersI mutationsaffect the expression of genes at both chromosome copies in diploid bacteria I codes for the regulatory factorrepressor protein which can diffuse throughoutthe cell hencetrans across beyond through and bind to operators regardless of their chromosomal locationcConstitutive mutation OclacIproductrepressor cannot bind to Opromoter always open to RNAPcPresence of Onormal O in plasmid does not compensate for Omutation on bacterial chromosomeBeta gal normal chromosome will be constantly producedOperator is cis acting elementO mutationsaffect only expression of the genes to which they are physically attached hence cison the same side asgenes on the same DNA chromosomeO is a specific DNA sequenceSecond Level of ControlOf the lac operon transcription initiationInteraction of cyclic AMP cAMP CAP complex with RNAPPositive regulation of lac operon when cell is starving no glucoseInvolves an activator proteinknown as CAPcatabolite activator protein or CRP cAMP receptor protein NOTES FROM LECTURES Page 1
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