User:James Chappell/ SigmaB
|Phase 1 - Promoter and RBS characterisation|
|Characterisation of Light Induced Promoter - Light induced expression of GFPmut3b and constitutive expression of the blue light receptor YtvA,||Characterisation of Clutch - The clutch protein EpsE under control of an inducible promoter,||Characterisation of Biomaterial Production - The two biomaterials combined with two signal peptides under control of an inducible promoter,|
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 .
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. 
- Boylan SA, Rutherford A, Thomas SM, and Price CW. Activation of Bacillus subtilis transcription factor sigma B by a regulatory pathway responsive to stationary-phase signals. J Bacteriol. 1992 Jun;174(11):3695-706.
- Gaidenko TA and Price CW. General stress transcription factor sigmaB and sporulation transcription factor sigmaH each contribute to survival of Bacillus subtilis under extreme growth conditions. J Bacteriol. 1998 Jul;180(14):3730-3.
- Masuda S and Bauer CE. AppA is a blue light photoreceptor that antirepresses photosynthesis gene expression in Rhodobacter sphaeroides. Cell. 2002 Sep 6;110(5):613-23.
- Jäger A, Braatsch S, Haberzettl K, Metz S, Osterloh L, Han Y, and Klug G. The AppA and PpsR proteins from Rhodobacter sphaeroides can establish a redox-dependent signal chain but fail to transmit blue-light signals in other bacteria. J Bacteriol. 2007 Mar;189(6):2274-82. DOI:10.1128/JB.01699-06 |