Lecture 8 - Intro to bacterial gene regulation Flashcards
Define what is meant by regulation of genes
Express subset of proteins allowing survival in current conditions
What are the 2 types of gene regulation?
- Global responses = all/lots of genes eg starvation, DNA dmg, heat stress
- Specific responses = 1/few genes only when stimulus present, often high energy
Describe transcriptional level of control and give examples
- How well RNAP binds promoter and how often triggered
- Sigma factor promoter preference
- Repressors/activators binding DNA
Describe post-transcriptional level of control and give examples
- Occlusion of Shine Dalgarno (SD) sequence
- cis-acting secondary mRNA structure preventing ribosome binding
- trans-acting sRNA binding mRNA to stop ribosome binding
Describe post-translational level of control and give examples
- protein maturation = correct function and location
- Sequestration and degradation of regulatory proteins
Describe the structure of RNAP and what part of promoter it binds
- Holoenzyme with 5 subunits = 2x large beta and beta prime + 2x small alpha + 1x sigma70 initiation factor
- Binds -10 -35 spacer
What are sigma factors?
- Form reversible complex with RNAP
- Guides RNAP to promoter then releases to allow elongation
- Motif preference depends on difference spacing = how frequently they modulate expression
Describe sigma70/RpoD and its 4 groups. What other sigma factor class is there?
- Sigma54/RpoN
- Sigma70/RpoD = large, complex
- Group 1/RpoD = essential
- Group 2/RpoS = non-essential external stimuli
- Group 3/RpoH = non-essential alternative eg heat shock
- Group 4/RpoE = extra cytoplasmic factor for periplasmic signalling
List the functions of the 4 domains of sigma factors
- 1 = only sigma70/RpoD bc always expressed = autoinhibition
- 2 and 4 = essential, binds DNA motifs
- 3 = non-essential, forms spacer separating binding domains
What are riboswitches and what do they do?
Sensory RNA determining how mRNA’s 5’UTR is folded = transcription, half-life, translation
What is a regulon?
Genes in different locations controlled by same promoter for coordinated expression
What is encoded by the RpoH regulon?
Proteases and chaperones to remove misfolded proteins to survival heat shock (42C for 5mins)
What is strange about the peak of RpoH transciption that doesnt align with its heat shock function?
Heat shock after 5 mins, transcrip peaks at 20mins
Describe how RpoH is a riboswitch and how this explains the transcription peaks noted
Thermosensitive riboswitch = tertiary hairpin structure in normal growth -> secondary structure in heat shock to allow more translation without more transcription
Describe what happens to RpoH in normal growth conditions
- Low RpoH
- Tertiary structure blocks SD and degraded after 40sec half-life
- DnaJ/grpE/dnak complex + FtsH protease in membrane binds and degrades misfolded tertiary RpoH
Describe what happens to RpoH in heat stress
- Riboswitch to secondary mRNA structure = SD access and 4min half-life
- Binds more RNAP = transcrip of RpoH regulon
Describe how periplasmic heat shock is managed in G-ve bacteria, comparing normal conditions and heat stress
- Normal = sigmaE kept low by sequestration by RseA and B periplasmic sensors in membrane
- Heat stress = DegS protease unfolds and degrades misfolded proteins, YaeL protease releases RpoE from RseA and B, RpoE binds RNAP and induces stress response by RpoE promoters eg RpoH
