User:James Chappell/ SigmaB

Sigma B
Heat, ethanol, salt, acid, light or a depletion of energy can all result in the activation of stress responses. For the moderate stresses as mentioned above, the response is controlled by the sigma factor B (σB). σB controls upto 200 genes in B.subtilis which confer various responses such as oxidative stress resistance, which help the survival of the organisms. However, knock outs have shown no diverse phenotype under normal growing conditions. Exposure to extreme stress conditions results in the sporulation of the B.subtilis. However it has been shown that σB is not required for sporulation and clearly is only playing a role in the response to moderate stress conditions. In addition to response to stress, it appears that σB is activated by entry into the stationary phase. This could potentially be problematic if we chose to use the wilt-type blue light receptor from B.subtilis that depends on σB. If we were to use a σB promoter then we would have multiple inputs into our device in addition to light.

AppA
Within the AppA system the effect of light on gene expression is mediated through the repressor PpsR4. From the diagram it can be seen that the system is only light sensitive in anaerobic conditions, in these conditions exposure to UV (blue light) causes the disassociation of PpsR4 from AppA and allow the PpsR4 to bind DNA and cause repression.