1. DNA Recognition in Procaryotes by Helix-Turn-Helix Motifs

2. Lysogeny vs. Lysis

3. Lysogenic Lytic

5. Cro from phage-monomer

6. Cro from phage-dimer

8. Repressor from phage-monomer

9. Repressor from phage-dimer

10. helix-turn-helix

11. Cro - DNA recognition helices vs. 34 Å

12. Genetics + Structural Biology

14. Repressor from 434 phage-dimer

15. 10.2 Most bacterial repressors are dimers containing  helices that insert into adjacent major grooves of operator DNA Figure 10-13 Copyright (c) by W.H.Freeman and Company

16. 434 repressor-DNA binding BeforeAfter

17. 434 cro/repressor-DNA binding

18. 434 repressor-DNA binding

19. 434 repressor-DNA binding- specific interaction

20. 434 repressor-DNA binding- Non-specific interaction

21. Protein-DNA interaction in Helix-turn-helix

22. 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

23. However, if a repressor protein, a product of a regulatory gene, binds to the operator, it can prevent transcription of the operon’s genes. –Each repressor protein recognizes and binds only to the operator of a certain operon. –Regulatory genes are transcribed at low rates continuously. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Fig. 18.20b

24. trp repressor-monomer

25. trp repressor-dimer

26. trp repressor-DNA

27. 10.2 Ligand-induced conformational changes alter affinity of many repressors for DNA Figure 10-14 Tryptophan binding induces a conformational change in the trp aporepressor Copyright (c) by W.H.Freeman and Company

28. 10.2 DNase I footprinting assays identify protein-DNA interactions Figure 10-6 Copyright (c) by W.H.Freeman and Company

29. 10.2 Gel-shift assays identify protein- DNA interactions Figure 10-7 Copyright (c) by W.H.Freeman and Company

30. 10.2 The footprint of RNA polymerase and lac repressor on the lac control region Figure 10-8 Copyright (c) by W.H.Freeman and Company

31. 10.2 The lac control region contains three critical cis-acting sites Figure 10-9 Copyright (c) by W.H.Freeman and Company

32. 10.2 Positive control of the lac operon is exerted by cAMP-CAP Figure 10-16 CAP = catabolite activator protein Copyright (c) by W.H.Freeman and Company

33. lac repressor-monomer

34. lac repressor(tetramer)-DNA

36. CAP-DNA

37. 10.2 A space-filling model of cAMP- CAP bound to lac promoter DNA Figure 10-18 Copyright (c) by W.H.Freeman and Company

38. 10.2 Cooperative binding of cAMP-CAP and RNA polymerase to the lac contol region activates transcription Figure 10-17 Copyright (c) by W.H.Freeman and Company

46. http://www.biochem.ucl.ac.uk/bsm/prot_dna/prot_dna.html

47. http://www.biochem.ucl.ac.uk/bsm/DNA/server/