Ruf 3 - Main Points: Lecture 2 Different sigma factors...

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Main Points: Lecture 2 Different sigma factors recognize different consensus recognition sites in promoter, allows utilization of different promoters and transcription of different genes under different conditions Constitutive vs. regulated expression: housekeeping genes Repressors and activators Positive vs. negative regulation Concept of a operon: group of coordinately regulated genes, includes a promoter and regulatory sequences such as operator sites and activator binding sites Lac Operon: an example of both + and – regulation of gene expression Negative regulation: E. Coli make a repressor protein (made constitutively) which in the absence of lactose binds to the operator site in the lac operon. Binding of repressor inhibits RNAP. In the presence of lactose, an inducer (allolactose) binds to the repressor and changes the shape of the repressor protein so that it no longer binds well to the operator site. This relieves repression of the promoter.
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Cis vs. Trans In Genetics Cis --- cis mutations affect only the DNA molecule to which they are linked DNA elements can only function in cis Trans --- trans mutations exert their effects through the action of a factor that can diffuse to other sites. Proteins function in trans Effects of a mutant can be determined by adding wild-type copies to the system
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Possible Regulatory Mutants i- : mutant nonfunctional repressor protein I S : super repressor: cannot be inactivated by inducer O C : operator constitutive: cannot be bound by repressor p-: promoter mutant: nonfunctional promoter Cis or Trans?
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1. Predict the phenotype of a lac I mutant:
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This note was uploaded on 03/14/2009 for the course BIOL 97 taught by Professor Edinger during the Fall '08 term at UC Irvine.

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Ruf 3 - Main Points: Lecture 2 Different sigma factors...

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