The best way to show that you understand various regulatory pathways is to be ab
ID: 147151 • Letter: T
Question
The best way to show that you understand various regulatory pathways is to be able to predict what will occur if something in that pathway is no longer working. For the following scenarios, explain what effect you think each protein mutation will have on its regulated pathway. In your explanation, you will need to describe what is supposed to occur, in order to explain how that changes due to the mutation.
1. Two mutations which change the two trp codons in the leader mRNA sequence of the trp operon to arginine codons. Will arginine levels now be able to regulate the tryptophan operon? How?
2. A mutation in the sensor kinases V. harveyi, so that they can no longer bind to any autoinducer.
Explanation / Answer
ANSWER -1)
Yes and No, Arginine levels will affect regulation of Trp operon. But due to other mechanism of regulation by repressor Tryptophan levels will still affect tryptophan synthesis.
The Trp operon can be seen containing two parts, First is regulatory region containing repressor gene, operator and promoter region and leader sequence. The other is region and 5 genes for TRP E, D, C, B, A. Tryptophan is expressed continuously and works through negative feedback.
Tryptophan regulation is done by two components, First is the repressor and second is the leader sequence.
The Leader sequence contains four regions 1, 2, 3 and 4. Region 1 is the most important which determines whether 2 and 3 pair together or 3 and 4 pair together. If 3 and 4 pair they form an attenuator loop which functions a transcriptional terminator. If region 2 and 3 pair together nothing happens and transcription continues. Region 1 consists of 2 trp codons, If tryptophan is high ribosomes cover region near 2 such that 3and 4 pair together and transcription stops. If these codons were mutated to arginine. It will affect the transcription of Tryptophan genes downstream. If arginine concentration increases Charged tRNAs will increase. Ribosomes will bind to region 1 and cover region 2 . Thus allowing 3 and 4 to pair. This will halt transcription.
The repressor in Trp operon is an apo-repressor. It is expressed in an inactive form, by binding to Tryptophan it becomes active and binds to the operator site on operon. This prevents the binding of RNA polymerase and prevents transcription of gene. As the concentration of Tryptophan rises it binds to Repressor (which is also continuously expressed). This repressor then binds to operator to block formation of more tryptophan.
ANSWER-2-)
Auto inducers are low weight signaling molecules secreted by cells for intracellular communication. Sensor kinases detect the concentration of AIs by means of phosphorylation.
The auto-phosphorylation activity of sensor kinases is inversely proportional to the concentration of AIs. The higher concentration of AIs corelates to lower phosphorylation levels. LuxN and LuxQ are the two hybrid sensor kinases in V.harveyi. They transfer the signal to a common protein LuxU. The information cascade now lead to LuxO which is a regulator protein. Ultimately Phospho-LuxO is responsible for repression of LuxCDABEGH under low cell density.
A mutation in the sensor kinases will prevent the further cascade of signaling.
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