Team:Imperial College/Light

Light Sensing
{{Imperial/Box1|Stress Response| One the of the first responses that gram positive bacteria have to stress is to synthesis the family of σ{{sup|B}} stress proteins. This σ{{sup|B}} is an alternative RNAP subunit that confers the ability to recognize a new series of promoters, particularly the SigB operon. If we wish to use the σ{{sup|B}} promoter within our device we need to understand all the potential inputs that σ{{sup|B}} can respond to.

To the right is an abstract diagram showing how the σ{{sup|B}} is activated. As can be seen in the diagram the pathway is dependent on the antagonist relationship between kinase and phosphatase. Essentially this is an elaboration of two component signaling found in many bacterium and simple eukaryotic, where there is sensing, transduction and transcriptional control.

The input of stress is at various points and can be generally split into nutrient and environment stress response.

Nutrient Response
RsbP is the node for nutrient stress response. In conditions of low ATP and GTP RsbP. It is not known exactly how the RsbP responds to the signals, RsbP contains a PAS motif that in some regulatory systems can respond directly to changes in electron transport, proton motive force, or redox potential, changes that typically precede shifts in high-energy nucleotide levels.

Environmental Response
The physical stress phosphatase (RsbU) requires a second protein (RsbT) for activity. Stress is thought to initiate a process that triggers the release of RsbT from a large inhibitory complex composed of multiple copies of two protein species, RsbR (and/or its paralogues) and RsbS. The stress-derived signal driving RsbT release is unknown, but it fails to develop in B. subtilis lacking either ribosome protein L11 or the ribosome-associated protein Obg. RsbR, RsbS, RsbT, Obg and ribosomes elute in common high-molecular-mass fractions during gel-filtration chromatography of crude B. subtilis extracts.

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