Difference between revisions of "Team:Sydney Australia/Experiments"

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PROTOCOLS

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Agarose Gel Electrophoresis

Gel electrophoresis is used to separate DNA based on their size and mobility through agarose. It relies on the fact that DNA is negatively charged, and that a uniform electric field can be applied across the semi-permeable agarose gel.

For a 1% agarose gel:

1. Add 1 g of agarose to 100 mL TBE.

2. Gently mix and microwave heat until dissolved.

3. Prepare gel tray. Depending on the tank, use masking tape or end-formers to seal the two ends of the gel tray. If using end formers, seal the ends by pipetting a small volume of gel solution into the contact between the end formers and tank and allow to set.

4. Allow the gel solution to cool and add 0.5 µL of Gel Red and pour the gel into the gel tray. Alternatively, exclude the Gel Red and stain with Ethidium Bromide after running the gel.

5. Insert the well comb into the appropriate position in the gel.

6. Once set remove the comb, tape/end formers and place into electrophoresis chamber and submerge in TBE.

7. Mix samples with loading buffer (use 1:5 ratio of loading buffer to sample) and pipette into wells.

8. Apply 120-180V, depending on time constraints and desired resolution.

Heat-shock Transformation

Transformation is a technique by which DNA may be inserted into competent cells. Transformation occurs naturally when cells uptake and express exogenous DNA from their environment. Heat shock transformation uses a rapid change in temperature to cause plasmids to enter cells via pores in the membrane. The introduced DNA will often contain a marker gene (usually antibiotic resistance) so that successfully transformed cells can be grown on selective media (normally an antibiotic), which corresponds to the marker gene.

1. Set-up a heat-block or water-bath at 42°C.

2. Retrieve aliquots of cells from -80°C freezer. Thaw on ice.

3. Add 1 pg-100 ng (1 µL - 5 µL) of plasmid DNA into cell suspension.

4. Incubate tubes at 42°C for 30-45 seconds.

5. Return to ice and quickly add 1 mL of LB-broth. Incubate tubes for 1 hour on the 37°C shakers.

6. Spread-plate 100 µL of cells on LB media containing the appropriate antibiotic. Alternatively, the cells can be diluted or concentrated before plating. For instance, centrifuge the tubes, pour off supernatant, resuspend cells in the final drop remaining in the tube and spread-plate the last 100 µL of cells.

7. Incubate overnight at 37°C.

PCR

The Polymerase Chain Reaction is used to amplify segments of DNA to high concentrations as a screen for the presence of the target or for further manipulation. The following protocol is readily tweaked depending on the specifics of the template DNA, primers and polymerase of choice.

1. PCR of multiple samples is sped up significantly by making a master mix; the volumes below are for one 50 µL reaction, but the volumes would be multiplied by the number of reactions required and mixed together in a single tube. - 5 µL 10x Pfu buffer/NEB Thermopol Buffer - 1 µL dNTPs at 10 uM (final 200mM) - 1 µL primer (F) (final 0.5-1uM) - 1 µL primer (R) (final 0.5-1uM) - 40.5 µL sterile MQ water - 0.5 µL Pfu/Taq polymerase

2. Aliquot master mix into PCR tubes (49 µL) then add 1 µL of the template DNA. Alternatively, if performing a colony PCR, aliquot 50 µL of master mix into a tube and resuspend cells directly from the plate into the tube. (Only dip the toothpick 3-5 times in the master mix).

3. Start the thermocycler at the setting desired. Cycles must have a peak high enough to denature template DNA, a trough low enough to allow annealing of primer pair, followed by an intermediate stage for the optimal polymerase activity. NB. Keep enzyme on ice and return to the freezer ASAP.

Plasmid Mini Prep - 100 mL

This is the process used to extract plasmids from bacterial cells. Plasmids can then be used for screening or further manipulation.

1. Pellet 100 mL culture in 2 x 50 mL Falcon tubes. Resuspend cells in 4 mL TE buffer, combine resuspended pellets in one tube.

2. Add 8 mL lysis solution (SDS-OH), mix well by inversion and shaking(~10 sec). Should go viscous. Leave at room temp for 15 min.

3. Add 6 mL ice-cold precipitation solution (K.Ac). Shake briefly – essential that K.Ac is thoroughly mixed in. Viscosity should disappear, and white precipitate appears. Keep on ice 15 min.

4. Spin at top speed (4000 rpm) in cold Centaur centrifuge for 15 min. Recover tube immediately and handle gently (pellet is soft and easily resuspended). Pour supernatant into new tube. Try to avoid the white junk, but don’t worry if little bits of it get transferred.

5. Add an equal volume isopropanol (~15 mL), mix well ice 15 min.

6. Spin at top speed (4000 rpm) in Centaur centrifuge (doesn’t need to be cold) for 15 min, pour off supernatant, keep pellet.

7. Add 10 mL 70% ethanol to pellet, resuspend by brief vortexing, leave for 5 min at room temp. Spin 15 min in Centaur centrifuge (doesn’t need to be cold). Pour off supernatant again.

8. Drain off excess supernatant by gentle tapping on paper towel, then heat at 50°C for approx 10 min to remove ethanol and isopropanol.

9. Redissolve pellet in 2 mL TE with mixing (tapping tube ~ 1 min , don’t vortex too much from this point onward). Can heat if necessary (eg. 50°C, 10-30 min). Note that plasmid DNA is much more soluble than chromosomal DNA, and dissolves preferentially. Solution should look slightly viscous (traces of chromosomal DNA still present).

10. Split prep into 2 x 1 mL in Eppi tubes. Extract each tube with phenol: chloroform: isoamyl (PCI), as follows. Suck up 500 µL PCI from under the aqueous layer in the reagent bottle, transfer to Eppi tube. Vortex for ~5-10 sec until a uniform milky white emulsion is obtained. Centrifuge 5 min. Transfer top phase (aqueous) to a new Eppi tube. Discard bottom phase (PCI) into phenol waste. Avoid the white junk at the interface between phases.

11. Repeat solvent extractions using 500 µl chloroform:isoamyl (CI, µl) per tube, as described for PCI above. After mixing & centrifugation, keep top aqueous phase, discard bottom CI phase into waste.

12. Split DNA prep into 4 equally sized aliquots (~400 µl each) Precipitate DNA by adding 1/10-volume 3M Na-acetate (~40 µl) to each tube, and then add 2 volumes cold ethanol (~1 ml). Incubate >2 hr at -20°C (overnight is fine).

13. Spin for 10 min, drain off supernatant, rinse pellet with 70% ethanol (as above, but using 500 µl 70% EtOH), drain excess EtOH off, then dry 10 min at 50°C.

14. Redissolve plasmid in 100 µL EB. Expected yields range from approx 10 µg plasmid per ml culture (eg pUC/pGEM) down to 0.2 µg plasmid per mL culture (eg. RSF1010). Final expected DNA conc. may range from approx 10-500 ng/µL.

Solutions: (see Sambrook Appendix 1)

• TE (solution I): 10 mM Tris, 10 mM EDTA, pH 8. Autoclaved.

• Lysis sol’n (solution II): 0.2 M NaOH, 1% SDS. Prepare fresh from separate stocks (NaOH – 2 M, Autoclaved ; SDS – 10%)

• Precipitation sol’n (solution III): 3 M potassium, 5 M acetate, pH 4.8. Autoclaved.

• Na-acetate: 3M, pH 4.8 (adjust with conc. acetic acid), autoclaved.

• EB (Elution buffer): 5 mM Tris, pH 8. Autoclaved.

NOTE: RNAse can be added to TE buffer at the start, or to the EB/TE at the end. RNA doesn’t interfere with most things, but can make gels look messy and obscure small DNA bands. Add RNase from conc., boiled stock (10 mg/ml) to final conc. of ~100 µg/ml. Back to top Preparation of Common Solutions LB media LB media is a common growth media used for the propagation of bacterial cells. 15. Mix 10 g Tryptone, 5 g Yeast extract, 5 g NaCl and 1 L of water, or use the same ratio in the required volume. 16. Autoclave the solution to sterilise. 17. Antibiotics can be added to make the media selective for antibiotic resistant cells. This must be added after autoclaving.

QiaQuick DNA Purification Kit

Working with DNA often involves adding enzymes (polymerases, restriction enzymes, ligases), which may subsequently need to be removed before they prevent or contaminate the next stage of work. DNA purification is pretty quick and easy using a store-bought Kit. Also consult the instruction booklet that comes with the Qiagen kit – the protocol below only gives the bare essentials required. This protocol below is good for restriction fragments, plasmids, and PCR products. It is NOT good for genomic or chromosomal DNA, which is too big to stick to the column effectively. Use the FastPrep reagents or CTAB-phenol type prep instead for genomic DNA.

1. Mix your DNA sample with the appropriate buffer, in the appropriate ratio: - DNA < 4 kb: Mix 1 vol sample with 3 vol of QG buffer. - DNA > 4 kb: Mix 1 vol sample with 3 vol of QG buffer + 1 vol isopropanol. - PCR products: Mix 1 vol sample with 5 vol PB buffer.

2. Load the mixture onto a Qiaquick spin column (purple) and spin 30 sec. Discard the flow-through, and replace spin column in the catch tube. The spin column will hold a max. of 800 µL sample and has a max. binding capacity of approx 10 µg DNA. You can wash through multiple 800 µL aliquots of DNA+QG if you have a lot of sample, so long as the total amount of DNA added doesn’t exceed approx 10 µg per column.

3. Add 750 µl of buffer PE to the column, allow to sit for ~2 min, then spin 30 sec, discard flow-through, replace spin column in catch tube.

4. Spin again for 30 sec to remove all traces of PE from the column. Discard both the flow-through and catch tube, and transfer spin column onto a clean Kimwipe. Leave the column lid open. Transfer Kimwipe to 50°C incubator box, and allow to dry for 10 min.

5. Transfer spin column to a sterile 1.5 mL Eppi tube, and add 50 µL* of EB buffer (5 mM Tris, pH 8) to the centre of the spin column – ie on the membrane, not the walls of tube. Allow to sit for 5 min. Spin 30 sec, retain Eppi tube with DNA solution in EB, discard spin column.

• Can reduce this to as little as 20 µL EB to give a more concentrated DNA solution, but keep in mind you will lose approx 3-5 µL EB during the procedure.

Restriction Digest

Restriction digestion employs restriction enzymes which recognise specific sites in a DNA sequence and will cut the strands at those sites. This may be used for diagnostic purposes by separating DNA into fragments of predictable lengths or for assembly by generating short overlaps at the restriction sites.

1. Add 5 µL of appropriate 10x buffer to a microcentrifuge tube. The buffer choice depends on the restriction enzyme used and can be checked from readily available tables.

2. Add DNA sample solution (~1 µg DNA).

3. Make tube up to 49 µL with reverse osmosis water.

4. Add restriction enzyme; 10 U activity is sufficient, which is normally the activity of 1 µL restriction enzyme solution. The restriction enzyme volume should not be more than 1/10 of the total reaction volume.

5. Incubate for an hour at the optimal temperature for restriction enzyme activity; again, this should be checked from relevant data tables. Restriction digests with two enzymes simultaneously are also possible and were performed over the course of the project. This involves the same protocol as above except that the reaction mixture is made up to 48 µL in step 3. This is only possible if the enzymes have compatible reaction buffers and optimal temperatures; if they do not, then you must perform two sequential digests with a purification step in between (see QiaQuick DNA Purification Kit protocol)