- Determine the concentration of the DNA sample by running both the vector and insert ona 1% agarose gel and comparing the bands intensity with the ladder (concentration known).
- Calculate how much solution is needed to obtain desired total amount of DNA for digestion.
- The volume of DNA solution can be no more than 70% of the total solution. Therefore calculate the total volume of digestion (probably around 20µl or 30µl).
- Transfer the DNA, BSA, the appropriate buffer and ddH2O into a microcentrifuge tube. Finally, add the enzymes to the solution. N.B. The enzymes should be kept on ice before being added to the digestion.
- Incubate for 60-90min at 37°C.
- Use gel electrophoresis to confirm correct digestion.
- Gel purification can be used to obtain the desired digestion product from the gel.
A typical ligation reaction mixture is around 10 μl and contains
- 1 μl DNA T4 ligase
- 1 μl DNA T4 ligase buffer (check to ensure it contains ATP) (10x)
- Purified, linearised vector*
- Purified, linearised insert*
- There should be a ratio of 6:1 for moles of insert to vector. This can be calculated using the following equation:
Insert mass (ng) = 6 x (Insert length (bp)/vector length (bp) x Vector mass (ng) Once the solution is made up, the tubes are vortexed and then spun down for around 10 seconds in a microcentrifuge. The ligation is done at 14°C in a water bath in the cold cabinet, and is left overnight.
E. coli Transformation
- One 15ml tube for each sample, in addition to one for a negative control, is put on ice.
- Tubes containing 1ml LB were incubated in a waterbath is set to 42°C .
- Between 25µl and 40µl of competent cells is transferred to each tube.
- The cells are left on ice for 10min.
- 5µl of the DNA sample are transferred into each tube, but ddH2O is added to the control tube(s). The liquids are added directly into the cell culture.
N.B. During pipetting the sides of the tube should not be touched to avoid contamination. Bubbles should be avoided because they can cause the cells stress.
- The tubes are transferred into the 42°C water bath for exactly 45 seconds and then put on ice for 2 minutes. Timing must be exact.
- The tubes are put on a rack and 1ml LB is added to all of them. This levels the temperature of the solution at about 37°C.
- The tubes are then put into a shaking incubator at 37°C for 1 hour.
- The solution from the 15ml tubes is then transferred to a microcentrifuge tube and spun at 13500 rpm for a few seconds.
- The supernatant is discarded and the remaining LB is mixed with the pelleted cells. This increases the concentration of the cells in the LB.
- 50 – 100μl of this solution is then pipetted onto chloraphenicol plates and left overnight at 37°C. The next day colony PCR can be used to examine if the transformation was successful.
Single Colony PCR (SCP)
A master mix is generally used for SCP, as well as Taq polymerase because the high error rate is not an issue here as it is purely confirmatory. Cells from an individual colony are first spread onto a replica plate, and the same loop is then used to inoculate a microcentrifuge tube containing 100μ ddH20 which will later be heated to 95°C to be used in the SCP (the same loop is finally used to inoculate LB for the overnight cultures). The protocol for the first SCP was as follows:
- 19.75μl ddH20
- 2.5μl Barnes buffer
- 1μl template (this comes from the tube that contains 100μ ddH20 and was inoculated with cells.
- 0.5μl dNTPs
- 0.5μl forward primer
- 0.5μl reverse primer
- 0.25μl Taq polymerase.
We also used a positive control (other DNA to which the primers will not anneal) and a negative control (ddH20).
The temperature cycle was as follows:
- 95°C for 30 seconds
- 30 cycles of:
95°C for 30 seconds
62°C for 90 seconds
68 °C for 30 seconds
- 68°C for 10 minutes
- Hold at 4°C
Tubes containing 5ml of LB medium are inoculated with cells from one colony and then 5μl of antibiotic (for example chloramphenicol) is added. They are then left at 37°C overnight.