Characterizing the cpxR promoter's response to varying temperatures over different time periods
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<h3><u>Protocol:</u></h3>
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The cpxR promoter was constructed upstream of an RFP construct (BBa_I13507). Top 10 competent cells were transformed with k135000-I13507 plasmids and plated. 5 ml overnight cultures were made from 5 different colonies using LB broth with appropriate antibiotics. Each of these cultures were aliquoted into six different tubes containing 600 µL of culture. These tubes were then placed in hot water baths at 30 C, 37C, 42C, 47C. Measurements were taken every hour for 5 hours after placing the tubes in different temperatures at 555 nm excitation and 632 nm emission.</p>
<p>Figure 3: RFP output produced by the CpxR-I13507 system when the system is heat shocked at different temperature for different lengths of time. The RFP output was measured at 555 nm excitation and 632 nm emission frequencies
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<h3><u>Discussion of Results and Conclusion</u></h3>
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This graph shows that the CpxR system does respond to temperature activated stress. When the system is placed at 42 C the RFP output is much higher at t=0 compared to the system placed at 37 C or 30 C. This indicates that the system does get activated due to heat shock which matches the literature parameters. At 47 C, the system gets activated faster because the linear regression has a steeper slope. This indicates that the system is being stressed and it produces its downstream product which is RFP in this case and DegP and other chaperones in the genomic DNA much faster in order to cope with periplasmic protein denaturation. Also, it seems that the system gets activated dramatically after 3 hours regardless of the temperature, this could indicate that the system peaks after 3 hours and the genomic CpxR produces enough downstream chaperones and proteases in order for the system to be able to cope with stress which allows the RFP reading to decrease at 4 hours time because the cell reaches homeostasis. This allows the cell to get rid of misfolded protein and other factors that might be contributing to stressing it out and causing the Cpx regulon to be activated. The cell then shows a rapid rise again because it is still under heat shock stress. But, if the cell was placed at 37 degrees, the cell would show a flatline pattern rather than an oscillating pattern.
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Revision as of 00:13, 30 October 2010
pCpxR (CpxR responsive promoter)
This is an adhesion responsive promoter (specifically adhesion to hydrophobic surfaces), and can be used to upregulate downstream gene expression in response to adhesion to such surfaces. It contains the binding site for CpxR-P (phosphorylated CpxR). CpxR is one member of the two-component Cpx response to envelope stress. Briefly, envelope stress causes CpxA, an inner-membrane histidine Kinase to Phosphorylate CpxR, allowing it to bind to CpxR-P responsive regions and regulate downstream target genes. See references for further information.
