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Transition to the open complex and high level of

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Unformatted text preview: stable closed complex b) The activator interacts with polymerase to trigger transition to the open complex and high level of transcription A DNA-bending protein can facilitate interaction btw distantly bond DNA bindingCooperative binding of proteins proteins (binding site is to (a) adjacent DNA sites bwt the activator binding site and (b) separated DNA sites and the promoter) The direction of the bend must be favourable for activation THE HELIX-TURN-HELIX MOTIF AS A DNA-BINDING ELEMENT Binding of a protein with a typical helix-turn-helix motif to DNA The protein typically binds as a dimer, and the two subunits are Indicated by the shaded circles. “R” is the recognition helix When E. coli grown on Glu + Gal -> rapid growth If Glu is exhausted growth levels off then picks up again During the lag, cells are turning on the lac operon to make enzymes to metabolize Gal LacZ encodes β-galactosidase (breaks down lactose) LacY – encodes permease (transports lactose into the cells) LacA – encodes transacetylase (unclear function) Polycistronic message = transcribed together from one promoter, turned on and off together THE OPERON THE • JACOB & MONOD: invented “operon” concept, the unit of bacterial gene expression & bacterial regulation regulation -includes structural genes -includes and DNA control elements recognized by regulatory gene products gene • cis-acting elements: DNA to -acting which operon is linked operon (doesn’t encode protein (doesn’t product) product) • trans-acting elements: acting diffusible regulatory products diffusible Jacob Monod lac OPERON OPERON Lewin Genes VII 2000 Oxford University Press Weaver 2002 Molecular Biology Ed. 2 • • • Jacob & Monod developed lac operon as THE classic paradigm for Jacob lac THE coordinate control of genes with related function coordinate lacZYA induced 1000-fold when lactose present induced lacZ-cleavage of lactose, lacY-transport of lactose into cell, lacA-cleavage lacY-transport lacA lactose acetylation lac OPERON REGULATION: overview overview lac INDUCER INDUCER • operon...
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