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. 负控诱导系统 正控诱导系统

6. 正控阻遏系统 负控阻遏系统

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

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

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

11. 2. No Inducer p t lacI lacZ lacY lacA o Repressed Repressor binds to lac o transcript Animation

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

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

14.  Attenuator 3. The Attenuation Mechanism of trp Operon  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. 1. The Regulation of ara Operon (1) organization 6.4 The Regulation of Other Operons P t P t araC araB araA araD Activator/ Repressor I 1 I 2 AraC dimer CRP O2O2 O1O1

19. Arabinose absent →Negative control araB A D O 1 CRP araI araC O2O2 PCPC P BAD Blocked

20. Arabinose present → Positive control araB A D O 1 CRP araI araC PCPC P BAD O2O2 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 Blount KF, Breaker RR. Riboswitches as antibacterial drug targets". Nat Biotechnol, 2006, 24 (12): 1558-64. 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.

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

27. Early Middle Late

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

29.  Committed.  Lysogeny  Lysis

30.  Execution  Lysogeny

31.  Lysis

32. 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 6.7 Post-Transcriptional Regulation

33. Summary 1. Concepts Gene ExpressionOperonAttenuator Constitutive ExpressionInducible OperonAttenuation Regulated ExpressionRepressible OperonRiboswitch Gene Regulation 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