"
Team:Cambridge/Experiments/Assembly of Reflectin Constructs
From 2011.igem.org
(→Results) |
(→Results) |
||
| Line 99: | Line 99: | ||
===Results=== | ===Results=== | ||
| - | After overnight incubation at 37°C of transformed ''E.coli'' cells, we could see colonies on only some of our plates. We examined successful plates under a fluorescence microscope to check if the cells had been transformed with a carry-through of the template DNA used in the initial PCR reactions. The risk of contaminating Gibson Assembly reactions with template DNA was fairly high because circular DNA of around 4kb was likely to co-localize with the linear PCR products. | + | After overnight incubation at 37°C of transformed ''E.coli'' cells, we could see colonies on only some of our plates. |
| + | We examined successful plates under a fluorescence microscope to check if the cells had been transformed with a carry-through of the template DNA used in the initial PCR reactions. The risk of contaminating Gibson Assembly reactions with template DNA was fairly high because circular DNA of around 4kb was likely to co-localize with the linear PCR products. | ||
{| border="1" align="center" style="text-align:center;" | {| border="1" align="center" style="text-align:center;" | ||
Revision as of 14:35, 26 August 2011
This is a placeholder. We should fill it in.
Contents |
Construct Design
Primer Design
We should mention expected lengths of products here.
Assembly: first attempt
PCR
In the first round of PCR, we amplified fragments required for the assembly of GA1, GA2, GA3 and GA4 constructs.
- We performed PCR using Phusion Hot Start DNA Polymerase in 20 μl reaction volume.
- The time profile used in the PCR machine was the following:
| Hold | 95°C | 2 min | |
| Cycling | Denaturing | 95°C | 10 s |
| Annealing | 55°C | 20 s | |
| Elongation | 72°C | 150 s |
We decided to use the 55°C annealing temperaure, although the predicted temperature for most primers is 5-10°C higher, because of a low annealing temperature of the VF2 primer.
- Primers and template DNA provided by our supervisor Paul served as a positive control, but eventually we did not detect any products on the gels.
The pictures below present result of gel electrophoresis of PCR products.
- In most cases position of a band matches the expected length of DNA fragment. The only exception are GA1-2 and GA3-2 products. According to the position on the gel the length of these DNA fragments is 4-5kb, whereas the predicted length is 3.5kb. Our hypothesis is that we were provided [http://partsregistry.org/Part:pSB1AK3 pSB1AK3] backbone instead of [http://partsregistry.org/Part:pSB1A3 pSB1A3] backbone.
- For GA1-1, GA2-1, GA3-1 and GA4-1 we obtained two bands: 1000bp and 400bp, with the latter resulting from non-specific priming most probably. We extracted the two bands for GA1-1, GA2-1 and GA4-1 products, labelling the 1000kb and 400bp fragments GAX-1a and GAX1-b respectively.
- The molecular weight marker that we used in all gels is HyperLadder I, which produces regularly spaced bands ranging from 200 to 10,000bp.
For the gel extraction of DNA we followed the protocol, assuming that one slice of gel is 100μl.
Gibson Assembly
We conducted Gibson Assembly of GA1, GA2, GA3 and GA4 constructs according to [Team:Cambridge/Protocols/Gibson_Assembly#Practice | the protocol]. The volumes of Master Mix and solutions of amplified DNA were the following:
| GA1 | GA2 | GA3 | GA4 |
|---|---|---|---|
| 15µl Master Mix | 15µl Master Mix | 15µl Master Mix | 15µl Master Mix |
| 2.5µl GA1-1a | 1.67µl GA2-1a | 2.5µl GA3-1 | 1.67µl GA4-1a |
| 2.5µl GA1-2 | 1.67µl GA2-2 | 2.5µl GA3-2 | 1.67µl GA4-2 |
| 1.67µl GA2-3 | 1.67µl GA4-3 |
Transformation
We transformed competent E.coli cells according to [Team:Cambridge/Protocols/Transformation_of_E.Coli | the following protocol]. We cultured each class of transformants on four different plates.
| GA1 and GA3 | GA2 and GA4 | |
| Plate 1 (10μl of cell suspension) | LB + ampicillin | LB + kanamycin |
| Plate 2 (100μl of cell suspension) | LB + ampicillin | LB + kanamycin |
| Plate 3 (10μl of cell suspension) | LB + ampicillin + arabinose | LB + kanamycin + arabinose |
| Plate 4 (100μl of cell suspension) | LB + ampicillin + arabinose | LB + kanamycin + arabinose |
Results
After overnight incubation at 37°C of transformed E.coli cells, we could see colonies on only some of our plates. We examined successful plates under a fluorescence microscope to check if the cells had been transformed with a carry-through of the template DNA used in the initial PCR reactions. The risk of contaminating Gibson Assembly reactions with template DNA was fairly high because circular DNA of around 4kb was likely to co-localize with the linear PCR products.
| Type of plasmid | Expected phenotype of transformed colonies | |
| LB + Antibiotic | LB + Antibiotic + Arabinose | |
| Reflectin A1 expression plasmid | No fluorescence | No fluorescence |
| I13520:pSB1A3 plasmid | No fluorescence | RFP red fluorescence |
| J69511:pSB3K3 plasmid | GFP green fluorescence | GFP green fluorescence |
| GA1 | GA2 | GA3 | GA4 |
|
Thus, we decided to conduct a series of tests to identify the cause of the failure. The proposed sources of error included:
DiagnosticsIn order to check if gel extraction of DNA was successful, we ran a 1% agarose gel with samples of purified products of the initial PCR reactions. Although we could see distinct, fairly thick bands on the first gels, from which components of Gibson constructs were purified, bands on the diagnostic gel are very faint, even missing in some lanes. This indicates that the yield of our extraction procedure was very low. Assembly: second attemptPCRIn the second round of PCR, we amplified fragments required for the assembly of GA1, GA2, GA3, GA4 as well as GA5 and GA6 constructs. We ran PCR products on a 1% agarose gel to separate amplified products from template DNA and primers, as well as to check how efficient and specific the amplification process was.
Gibson AssemblyTransformationResultsWhat next?
|
