Flip One Pancake

From 2006.igem.org

Revision as of 16:26, 13 June 2006

Flipping One Pancake

Plan A: Flipping the Coding Region

The plan is to construct a plasmid that contains the following. Recombination would be detected as production of Tet resistant colonies.

1. Amp resistance gene as in pSB1A3
2. Hin recombinase gene driven by lacP (inducible in JM109 by IPTG or lactose)
3. RE (recombination enhancer)
4. One Pancake test construct:

araBAD promoter, inducible with arabinose
RBS
hixL recombination site
CDS for Tet resistance in reverse direction
hixR recombination site
double forward terminator, BBa_B0015 Plate DNA-1, Spot 1I

Plan B: Flipping the Promoter

The plan is to construct a plasmid that contains the following. Recombination would be detected as RFP expression.

1. Amp resistance gene as in pSB1A3
2. Hin recombinase gene driven by lacP (inducible in JM109 by IPTG or lactose), cloned from PCR product by Davidson team
3. RE (recombination enhancer), synthesized by Davidson team
4. One Pancake test construct:

hixL recombination site
araBAD promoter, inducible with arabinose BBa_I13453 Plate DNA-2, Spot 13D
hixR recombination site
RBS, CDS for mRFP, double forward terminator, BBa_I13507 Plate DNA-1, Spot 16N

Building A House of Pancakes, in the Fewest Steps Possible

We are going to start with Plan B: Flipping a Promoter This has the most parts ready to go.

• We need to know how to put the Hix sites around the promoter and coding regions so we can build things one time only.
• What would it take to create coding regions or promoters that are in both orientations? If we use the NotI method, can we continue to add onto them with the reversed and modified BB ends?
• Using Ara promoter is a good idea so we can separate transcription from flipping.
• We need to use PCR to amplify the Tet, Chloramphenicol, Kanamycin resistance genes.
• We will need these +/- Hix sites. Do we need them with terminator included? Probably to keep things simple. Alternatively, we could leave TT at the end and never flip it.
• Do we need to compare with low copy number plasmid?

Control Experiments For One Pancake Flippin'

• We need to test Lac promoter in front of Hin (with RFP downstream perhaps for easy measuring?)
• We need to test Ara Promoter +/- AraC.
• We need to test Ara Promoter with Hix sites +/- AraC.
• We need to flip a promoter with no stuffer DNA.
• We need to flip a promter with stuffer DNA so it is about 1 kb total length.
• We need to flip coding region of about 1 kb in length downstream of a non-flippable promoter.
• We need to see if flipping stops on its own.
• We need to see if chloroquine can regulate flipping.
• We need to see if we can measure kinetics of flipping (i.e., how fast does it start once we induce Hin?).

Flipping Procedure (draft)

1. Grow JM109 in minimal media to exponential (A600 = 0.5?)
2. Induce Hin recombinase with IPTG (how much, how long?)
3. Allow recombination (how long?)
4. Turn off recombination by spinning down, resuspending with no IPTG
5. Induce araBAD promoter and Tet resistance with arabinose (how much, how long?)
6. Spread on Amp plates first, then replica plate on Tet plates, look for resistant colonies

Flipping To Do List

1. Plasmid prep pSB1A3, digest with EcoRI + PstI, Pase, gel purify
2. Anneal hixL, hixR, and hixC oligos, then ligate into vector, transform
3. Start overnights from colonies for double forward terminator, pBAD, mRFP
4. Decide on resistance gene to be flipped, do transformations
5. Design PCR primers for 3 drug resistance genes (Not Amp^R). Amplify and clone into BioBrick plasmid.