3.20.07 - 3.20.2007 F' I+ P+ O+ Z+ Y- A+ / I+ P- O+ Z+ Y+...

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3.20.2007 F I + P + O + Z + Y - A + / I + P - O + Z + Y + A + o RECAP: o LacI-: repressor can’t bind operator o lacIs: repressor can’t bind allolactose can function in trans to regulate genes on a different DNA molecule o lacOc: operator can’t bind repressor bad binding site for the repressor so operator remains unoccupied o lacZ-: nonfunctional B-galactosidase o lacY-: nonfunctional permease o lacA-: nonfunctional transacetylase o lacP-: nonfunctional promoter at lac operon o now look at B galactosidase from the plasmid (left side) Inducible Look at I+, it can bind to the operator when lactose is present and therefore alolactose is present the alolactose binds to the repressor, it changes shape and lets go of the operator, leaving it open so nothing blocks RNA polymerase from transcribing Possible that the I+ can be bound to the repressor when lactose and therefore alolactose are absent, no alolactose, this wild type repressor just sits there Therefore it is inducible o Now look at chromosome B-galactosidase Uninducible Look at the promoter, nonfunctional promoter, doesn’t allow expression of any of the genes connected with it, you can ignore all the genes it controls when it is P-, transcription is not possible here o Now overall what is the expression of beta galactosidase in the cell? You think it is inducible but…we can only pencil it in because if we say it is inducible we are saying that when lactose is available then the alolactose will bind to that repressor and pull it off the operator to allow expression and when lactose is absent and there is no alolactose the repressor will stay on the operator, the expression dependso n the concentration of alolactose, but you have to have lactose and PERMEASE to get alolactose Now you must check the expression of permease, leaky transcription is irrelevant, it will not be enough to get enough alolactose – must have inducible or constitutive permease for enough alolactose o So look at the permease expression in the plasmid: Uninducible o Permease in the chromosome Uninducible o Overall, for the cell permease is uninducible o So back to the overall expression of B-galactosidase is that it is Uninducible There is a wild type repressor that sits on a wild type operator but without alolactose *because of no permease* it cannot release from the operator, so it is uninducible o Would inducible expression of permease depend on alolactose? Need wild type operator, wild type repressor bound to it, so in absence of lactose and alolactose it sits there and prevents transcription…when they are available the repressor binds to it and allows for transcription Everything depends on alolactose, including permease and you have to have enough beta galactosidae to get alolactose which is necessary fro permease o Why is it possible to get permease constitutive when Bgal is uninducible If the operator is perpetually unoccupied due to an Oc regardless of alolactose, it wouldn’t matter
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This note was uploaded on 04/07/2008 for the course BIO 325 taught by Professor Saxena during the Spring '08 term at University of Texas at Austin.

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3.20.07 - 3.20.2007 F' I+ P+ O+ Z+ Y- A+ / I+ P- O+ Z+ Y+...

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