Chapter 6 Regulation of Prokaryotic Gene Expression

1. Chapter 6 Regulation of Prokaryotic Gene Expression

2. 6.1 Overview 1. What are Gene Expression and Regulation? (1) Gene expression • Constitutive Expression • Regulated/Adaptive Expression (2) Gene regulation/control

3. 2. Influencing factors  Nutritional status  Environmental factors  Hormone level  Developmental stage

4. 3. Operon (1) What is an operon? (2) Operon types Inducible operon  Repressible operon (3) Gene regulation of operon Negative regulation Positive regulation

5. 正控诱导系统 负控诱导系统

6. 正控阻遏系统 负控阻遏系统

7. Regulatory gene Structural Genes DNA lacI lacZ lacY lacA PlacI Olac Plac mRNA Protein repressor Transacetylase β-Galactosidase Permease 6.2 The Regulation of lac Operon 1. Organization of lac operon

8. 3. Positive control of lacoperon cAMP CAP (catabolite activator protein) or cAMP receptor protein (CRP)

10. 1. + Inducer (lactose/ allolactose) Induced Repressor cannot bind p p t t lacI lacZ lacY lacA o transcripts Repressor Permease Transacetylase -galactosidase 4. Negative contral of lac operon

11. 2. NoInducer Repressed Repressor binds to laco p t lacI lacZ lacY lacA o transcript Animation

12. 6.3 The Regulation of trp Operon 1. Organization of trp operon

13. 2. The Repression of trp Operon trpR→ Repressor Corepressor

14. 3. The Attenuation Mechanism of trp Operon Attenuator  Mechanism of Attenuation When Ribosome reaches Trp codon  Trp is scarce  Trp is aboudant

15. Attenuation model in Trp starved cells.

16. Attenuation model in Trp non-starved cells Animation

17. 5. Generality of Attenuation

18. P P t t CRP O2 I1 I2 O1 araC araB araA araD AraC dimer Activator/ Repressor 6.4 The Regulation of Other Operons 1. The Regulation of ara Operon (1) organization

19. Arabinose absent→Negative control O2 araC araB A D O1 CRP araI PBAD PC Blocked

20. O2 araC araB A D O1 CRP araI PBAD PC Arabinose present→ Positive control Transcription

21. 2. The Regulation of rRNA Operon (1) organization

22. 6.5 Riboswitches 1. What is a riboswitch? Riboswitches have two important domains:  an aptamer  an expression platform

23. 2. Mechanism of Riboswitches (1) Inhibition of Translation Initiation (2) Transcription termination (3) Auto-cleavage

24. 3. Tempting Targets

25. 4. Riboswitches and the RNA World hypothesis 5. Riboswitches as Antibiotic Targets Brantl, S. Bacterial gene regulation: from transcription attenuation to riboswitches and ribozymes. Trends Microbiol, 2004, 12:473-475. Mandal, M. and R. R. Breaker. Gene Regulation by Riboswitches. Nat Rev Mol Cell Biol, 2004, 5:451-463. Blount KF, Breaker RR. Riboswitches as antibacterial drug targets". Nat Biotechnol, 2006, 24 (12): 1558-64.

26. 6.6 Time Regulation 1. Time Regulation of Sigma Factors Different sigma factors recognize different promoters and thus, the availability of sigma factors can regulate the transcription of genes associated with these promoters. 

27. Early Middle Late

28. 2. Time Regulation of λ phage  Uncommitted.

29.  Committed. Lysogeny Lysis

30.  Execution Lysogeny

31. Lysis

32. 6.7 Post-Transcriptional Regulation 1. Translation Initiation of Regulation (1) Ribosome binding site (rbs) (2) SD sequencing (3) mRNA secondary structure (4) Initiational codon 2. Regulation of Rare Codon 3. Transcriptional Regulation of Overlapping Gene 4. Translational Repression

33. Summary 1. Concepts 2. Differences between inducible operon and repressible operon 3. The regulation mechanism of lac operon 4. The regulation mechanism of trp operon (attenuation) 5. The regulation mechanism of ara operon 6. The regulation mechanism of riboswitches

34. Thank You Very Much