RegulationHO10.pdf

1 411 Lecture Outline-12 Feb ?10 1.Strategies of regulation 2.Overview of RNA pol & Transcription Initiation 3.Represors vs. Activators of transcription 4.Control beyond represors/activators? Transcription regulation 1.Initiation of transcription ?change in ? factors ?direct stimulation by DNA sequence or structure ?use of represors ?use of activators Figure 2.3 A review of transcription in Bacteria? The Bacterial RNA pol has several subunits and functions as either the core or holenzyme form. Bacterial transcription RNA pol contacts many bases of DNA simultaneously; diferent contacts in ?Initiation (with RNA pol holoenzyme) ?Elongation (with RNA pol core enzyme) (Compare to Fig. 2.7) 2 Figure 2.6 Stereotypical bacterial promoter Promoter with this structure/sequence binds RNA pol holenzyme with ? 70 with high affinity. Diferent holenzymes bind to/initiate transcription from distinct promoters. RNA pol/DNA/RNA complex Figure 2.16 Figure 2.8 RNA pol & transcription cycle Figure 2.13 Holoenzyme contacts can enhance promoter recognition Panel A: Consensus promoters bind holoenzyme tightly? Panel B: When you absolutely, positively want to transcribe lots of RNA? 3 Figure 2.8 Initiation is multistep process Figure 2.10 Many opportunities to affect initiation of transcription? Figure 12.18 A different model of regulation: ara Thre loci revealed in mutational analysis. (The two not shown here neded for L- Ara transport.) Analysis of Ara mutants At least 4 complementation groups/genes (araA, araB, araC and araD) are defined by the Ara - mutants L-arabinose L-ribulose L-ribulose- 5- phosphate D-xylulose- 5- phosphate araA araB araD What about araC? AraC mutants can grow on xylulose, so it?s not further downstream. Is AraC a regulator? 4 araC - Mutants Are ?Super-represed? C - BAD OF OF No L-arabinose Plus L- arabinose What could be the function of AraC? It does not act like the LacI represor? C - BAD Figure 12.20 Action of AraC cAMP-CRP and AraC Figure 13.4 Beth Traxler RegulationHO10.ppt