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DNA Recognition in Procaryotes DNA Recognition in Procaryotes by Helix-Turn-Helix Motifsby Helix-Turn-Helix Motifs
Lysogeny vs. Lysis
Lysogenic
Lytic
Cro from phage-monomer
Cro from phage-dimer
Cro from phage-dimer
Repressor from phage-monomer
Repressor from phage-dimer
helix-turn-helix
Cro - DNA
recognition helices vs. 34 Å
Genetics + Structural Biology
Repressor from 434 phage-dimer
10.2 Most bacterial repressors are dimers 10.2 Most bacterial repressors are dimers containing containing helices that insert into adjacent helices that insert into adjacent
major grooves of operator DNA major grooves of operator DNA
Figure 10-13
Copyright (c) by W.H.Freeman and Company
434 repressor-DNA binding
Before After
434 cro/repressor-DNA binding
434 repressor-DNA binding
434 repressor-DNA binding-specific interaction
434 repressor-DNA binding-Non-specific interaction
Protein-DNA interaction inHelix-turn-helix
By itself, an operon is on and RNA polymerase can bind to the promoter and transcribe the genes.
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
Fig. 18.20a
However, if a repressor protein, a product of a regulatory However, if a repressor protein, a product of a regulatory gene, binds to the operator, it can prevent transcription of gene, binds to the operator, it can prevent transcription of the operon’s genes.the operon’s genes.– Each repressor protein recognizes and binds only to the Each repressor protein recognizes and binds only to the
operator of a certain operon.operator of a certain operon.– Regulatory genes are transcribed at low rates Regulatory genes are transcribed at low rates
continuously. continuously.
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
Fig. 18.20b
trp repressor-monomer
trp repressor-dimer
trp repressor-DNA
10.2 Ligand-induced conformational ch10.2 Ligand-induced conformational changes alter affinity of many repressors fanges alter affinity of many repressors f
or DNAor DNA
Figure 10-14
Tryptophan binding induces a conformational change in the trp aporepressor
Copyright (c) by W.H.Freeman and Company
10.2 DNase I footprinting assays ident10.2 DNase I footprinting assays identify protein-DNA interactionsify protein-DNA interactions
Figure 10-6
Copyright (c) by W.H.Freeman and Company
10.2 Gel-shift assays identify protein-10.2 Gel-shift assays identify protein-DNA interactionsDNA interactions
Figure 10-7
Copyright (c) by W.H.Freeman and Company
10.2 The footprint of RNA polymerase 10.2 The footprint of RNA polymerase and and laclac repressor on the repressor on the laclac control re control re
giongion
Figure 10-8
Copyright (c) by W.H.Freeman and Company
10.2 The lac control region contains t10.2 The lac control region contains three critical cis-acting siteshree critical cis-acting sites
Figure 10-9
Copyright (c) by W.H.Freeman and Company
10.2 Positive control of the 10.2 Positive control of the laclac operon operon is exerted by cAMP-CAPis exerted by cAMP-CAP
Figure 10-16
CAP = catabolite activator protein
Copyright (c) by W.H.Freeman and Company
lac repressor-monomer
lac repressor(tetramer)-DNA
lac repressor(tetramer)-DNA
CAP-DNA
10.2 A space-filling model of cAMP-CA10.2 A space-filling model of cAMP-CAP bound to P bound to laclac promoter DNA promoter DNA
Figure 10-18
Copyright (c) by W.H.Freeman and Company
10.2 Cooperative binding of cAMP-CAP and 10.2 Cooperative binding of cAMP-CAP and RNA polymerase to the RNA polymerase to the laclac contol region ac contol region ac
tivates transcriptiontivates transcription
Figure 10-17
Copyright (c) by W.H.Freeman and Company
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