IGEM:IMPERIAL/2009/Encapsulation/Timers
Timers
Timers have many biological and engineering appplications. Design of mechanisms and characterisation of parts will provide a reusable timer module.
We could have a timer module as part of Modules 1, 2, 3 or 5 of our project.
Previous iGEM teams have explored different genetic circuits required to produce a timer.
Considerations for our timer:
- Separate timer for each phase vs. one timer that is ‘continuous’ between phases
- Thresholds
- Periodicity
- Start/stop vs. oscillation vs. combination of both
- Reset function
- Pre-programmed function(s)
- James Chappell 05:34, 21 July 2009 (EDT):What would the specs for our timer be? You should try to identify these first then look at the existing timers and see if they meet the specs, if not then look for new designs. Also Might be good to add diagrams of how the circuits work.
Specifications for a Timer in Each Phase of our Project
Module 1 - Compound:
- Induce production of compound at a specific time? - eg in response to something.
Module 2 - Encapsulation:
- Induce sporulation/encapsulation once desired threshold of compound X has been produced.
Module 3 - Killing Strategy:
- Induce death after encapsulation.
- Have a preset timer that induces death once the bacterium is encapsulated? (Chiba'08)
- Induce death immediately - would a timer be required? Why not just use a promoter? We could set a threshold rather than using a timer mechanism.
Module 5 - Delivery
Previous iGEM Timers
Chiba2008
Linear accumulation of non-degradeable signal molecules over time, which are then detected by receivers.
KULeuven2008
KULeuven used the 'InverTimer' in their 'Dr. Coli' project to induce destruction of their bacteria once the time lapsing between disease signals had reached a sufficient period.
Their system is a LacI based inverter, controlling LuxI production. LuxI produces AHL (quorum-sensing molecule) which in turn gradually activats LuxR and its controlled promoter in the next module/device.
NYMU-Taipei2008
Taipei made two timers based on a three-component system:
Starter, Counter, Stopper
The counter component of the system is an oscillator. They required two timers with different periods so used different oscillators to fit the purpose of each timer.
Cyanoxilator
- A Cyanobacterial oscillator using the Kai proteins in E.coli.
- Time period of between 14 - 60 hours (...wide range there??)
Reloxilator
'A tuneable intracell-synchronized relaxation oscillator based on the combination of:
- Using the lysogenic genetic swtich from phage lambda and giving it tuneable oscillatory properties.
- Using the intracellular synchronising properties of Vibrio fischeri.
- Time period of ~46 minutes.
The timers are stopped once protein production reaches a pre-set threshold. Once this threshold is reached, the activity of the output promoter changes.
