linda - RNA based gene regulation and regulons Flashcards
(25 cards)
What is post-transcriptional control in bacteria?
Regulation of gene expression after mRNA synthesis but before translation begins.
What are small regulatory RNAs (sRNAs)?
Short non-coding RNAs (50–500 nt) that regulate gene expression by binding mRNA, affecting its stability or translation.
How do sRNAs regulate translation?
By interacting with the ribosome-binding site (RBS), they can either promote or inhibit translation.
What is RyhB?
An sRNA that regulates iron homeostasis in E. coli by downregulating iron-containing proteins under low iron conditions.
What role does Fur play in iron regulation?
Fur represses ryhB transcription when intracellular iron levels are sufficient.
What happens when iron is limited in E. coli?
Fur dissociates, RyhB is transcribed, and it represses synthesis of iron-requiring proteins to conserve iron.
What degrades RyhB when iron levels are restored?
RNase E degrades RyhB, allowing iron-dependent enzymes to be re-synthesised
What are antisense RNAs (asRNAs)?
RNAs transcribed from the opposite strand of a target mRNA that are fully complementary and inhibit translation.
How do asRNAs function?
They bind to target mRNAs to prevent translation into protein.
Example of asRNA regulation?
OxyS RNA inhibits translation of fhlA in response to oxidative stress.
Are sRNAs and asRNAs the same?
No. sRNAs are transcribed from separate genes and partially complement targets, while asRNAs are fully complementary and transcribed from the opposite DNA strand.
What is a regulon?
A group of genes involved in the same process, located in different chromosome regions, regulated together by a common mechanism.
How do regulons differ from operons?
Regulon genes have individual promoters and are not adjacent; operon genes are transcribed together under one promoter.
Give examples of regulons in bacteria.
Heat shock response, stringent response, SOS response.
What is the heat shock response?
A regulon-controlled mechanism where cells produce heat shock proteins (HSPs) in response to elevated temperature or stress.
What does Sigma-32 (σ³² / RpoH) do?
It initiates transcription of heat shock genes during temperature stress.
What happens to σ³² under normal conditions?
It is unstable and quickly degraded, so heat shock proteins are not produced.
What happens to σ³² during heat shock?
It stabilizes, leading to increased transcription of HSPs like DnaK, GroEL, and GroES.
What happens during recovery from heat shock?
σ³² is degraded again, and heat shock gene expression returns to baseline.
What is the stringent response?
A stress response to nutrient deprivation where the cell halts macromolecule synthesis and activates survival pathways.
What molecules signal the stringent response?
ppGpp (guanosine tetraphosphate) and pppGpp (guanosine pentaphosphate), also known as alarmones.
What enzyme synthesises (p)ppGpp?
RelA, which adds phosphate from ATP to GDP or GTP.
What is SpoT’s role in the stringent response?
It can both synthesise and degrade (p)ppGpp.
How does the stringent response help survival?
By shutting down ribosome production, DNA replication, and other energy-consuming processes.
