Lecture 22 Prok Gene Reg

Lecture 22 Prok Gene Reg - Prokaryotic Gene Regulation...

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Prokaryotic Gene Regulation Dr. Matera 16 Mar 2009 Lac repressor protein in violet, binds to specific sites in DNA  to turn off expression of the  lac  operon in  E. coli .  The  repressor is a tetramer with two subunits binding to  lac   operator binding sites 93 bp apart, causing the DNA to form  a loop. 
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Fig. 17.2 Prokaryotic transcription overview
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Outline and Concepts There are many steps in gene expression and regulation can occur at any one of them. In prokaryotes, much of the regulation affects the initiation of RNA transcripts. Bacterial genes that function in same pathway are often clustered and coregulated in the genome, forming operons . Operons illustrate concepts: Feedback Regulation Allostery Genes for lactose utilization – the lac operon Negative regulation – blocks transcription Positive regulation – increases transcription DNA binding proteins acting on RNA polymerase at promoter are main agents of regulation Cis-acting versus trans-acting elements
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Most organisms can use a variety of carbon sources, but prefer glucose – easily turned into ATP. Bacteria live in fierce competition, try to express only genes that are needed for growth. Monod et al. isolated many Lac - mutants that were to unable to utilize lactose . Complementation analysis identified three genes in a tightly linked cluster: Lactose utilization in  E. coli • LacY gene product (permease) actively transports lactose into the cell • LacZ gene product (beta-galactosidase) converts lactose into glucose and galactose (in a side reaction, it also converts lactose into allolactose, which functions as an inducer )
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Lecture 22 Prok Gene Reg - Prokaryotic Gene Regulation...

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