Final 20 Flashcards
What are the protein associated with SOS Response?
RecA and LexA
What is RecA and LexA do in the SOS response.
RecA binds to ssDNA and it acts as a “co-protease”
LexA is a repressor that is typically bound on SOS genes, so when RecA binds to ssDNA it will cause LexA to dissociate and cause self-proteolysis, activating those genes.
What is the Stringent Response? What is the signal for this?
It is a response to AA starvation and protein synthesis will come to a stop.
The signal is an uncharged tRNA molecule.
What are the three steps in the stringent response?
- Binding of an uncharged-tRNA molecule in the A site of the ribosome.
- Activation of the RelA stringent factor associated with the ribosome.
- Formation of an unusal nucleotide pppGppp which will bind to the beta-subunit of RNAP, inhibiting the open complex to form on the promoter.
The promoter that it has the largest affect on is the one associated with rRNA, it shuts down the synthesis of ribosomes.
What is cis regulation?
A molecule affecting its own function.
What is trans regulation?
A molecule is affected by another separate molecule.
Structural aspects of mRNA. Is this trans or cis actiing?
Cis-acting.
Explain how the structural aspect of mRNA can regulate gene expression?
Under normal conditions:
The SD of mRNA is hidden i na secondary structure, preventing ribosome activity.
Under hot conditions:
The secondary structure is removed and the SD becomes available for the RNAP to bind.
Riboswitches. Is this trans or cis acting?
Cis-Acting
What is a riboswitch?
It is a domain on mRNA that can bind a small molecule.
How does a riboswitch work?
Binding to a ligand affects the conformation of the mRNA and its activity (hides the SD)
Riboswitches allow for the mRNA to participate in its own regulatoin and it is regulated with the ligand that is produced by that gene.
Explain the example of a riboswitch in bacteria.
TPP binds to an aptamer, causing a conformation change, hiding the RBS.
- Terminator Hairpin
- Blockage- Steric Hinderance
- Splicing
RNAs participating in regulation. Trans or Cis regulating?
Trans-regulated.
How can RNAs affect gene expression? (3)
Regulatory RNAs usually interact with the target DNA through base-pairing.
- Disruption of Protein Binding
- Change in DNA structure
- Recruitment of Proteins
Are sRNA trans or cis acting?
Trans-acting.
What was one example of sRNA regulattion?
Sigma-s mRNA is presented at low levels, but it not translated due to a hairpin loop.
To get expression of sigma-s mRNA, sRNAs bind to the mRNA, inhibiting the formation of the hairpin loop, allowing for translation to occur by revealing the RBS.
This is aided by a chaperone protein Hfq.
