Memory effects of UV exposure
From 2006.igem.org
Contents |
Group III
Aim
We are interested in converting a transient UV exposure into a persistant response. We plan to achieve this by coupling UV response system to a bistable network. Such system can be used to monitor cells that have undergone UV damage.
Approach
So what is this UV damage response and why long term monitoring?
The SOS response
The SOS genetic network consists of various genes that perform diverse functions in response to DNA Damage NER (Nucleotide Excision Repair) Translesion DNA replication Homologous recombination Cell division arrest
RecA acts as a sensor of DNA Damage RecA gets activated and mediates LexA auto-cleavage
Transient response induced in response to DNA damage. The promoter activity increases rapidly in the first few minutes and decrease within an hour.
Thus, long time monitoring of DNA Damage induced by UV Irradiation requires that this transient signal generated is stabilized.
So, we tried to couple this transient signal to a bistable network to enable long time monitoring of DNA Damage.
We have used the lac regulatory network as the bistable network.
Constructs
Here comes the exciting stuff, the synthetic biology part! We have made the following parts
We have placed the lacY gene under the SOS (UV responsive) promoter. Since the production of Lac Y and the effect of build of Lac Y upon our memory switch would take time, we needed an immediate reporter of promoter activity . So the mRFP gene was also placed under the SOS promoter to make the final part - mRFP and LacY gene under the SOS promoter.
This is then transformed into the Muk21 strain to make the final UV circuit switch.
Upon UV exposure the SOS promoter is active and drives the production of Lac Y.(measurement of RFP fluorescence levels gives the immediate measure of promoter activity) The idea was to operate in the bistable region of the Muk 21 strain (based on TMG concentration) and thus in this region any change in the levels of Lac Y will drive the production of chromosomal GFP and thus cells that were UV damged would expected to be Green and others which didn't would be expected be non green .
Testing Bisability in the UV-switch strain
The regulatory network involved in uptake and utilization of lactose exhibits bistability over a range environmental conditions [Ozbudak et al., 2004]. This has been demonstrated in an E.coli strain Muk21 that has chromosomal integration of GFP expressed under lac promoter.
A bistable network is hysteretic. Environmental history determines state of the network at intermediate inducer concentration.
This is a scatter plot of cells. Cells with uninduced (lower panel) or induced (upper panel) history are grown in different TMG concentrations.
We transformed Muk21 with our UV-switch construct to test hysteresis which is a characteristic behavior of a bistable network.
This is a scatter plot of cells. Cells with uninduced (;eft panel) or induced (right panel) history are grown in different TMG concentrations.
