Protocols

Transformation Protocol in DH5α (Invitrogen)

Thaw an aliquot of competent bacteria on ice.

Add 50 µl of DH5α competent cells gently in a sterile 15 ml polypropylene tube.

Add 1 µl of ligation mixture or Gibson Assembly reaction (1 – 10 ng of DNA) to the polypropylene tube

Incubate on ice for 30 minutes.

Heat shock for 45 seconds in a water bath at 42°C, then quickly back on ice for 2 minutes.

Add 450 ml of room temperature SOC medium (Work sterile!!).

Incubate 1 hour at 37°C for antibiotic resistance expression, while shaking (225 rpm).

Spread 1/10 and 9/10 on LB plates (containing the right antibiotic).

Notes:

• Do not shake the polypropylene tubes during the heat shock!
• To increase the yield, centrifuge gently (at low speed), remove the excess of medium and then spread on the plates.
• To determine transformation efficiency

Gel Electrophoresis

Dissolve 2g of Agarose in 200 ml TAE or TBE buffer. Heat until the solution is clear. Do not boil.

Allow to cool down and add 2µl of ethidium bromide.

Transfer to the casts + combs and leave at room temperature. Store at 4˚C for later use.

Input:

• 5 µl DNA ladder
• 5 µl sample + 5 µl H2O + 1 µl loading buffer

Preparation of LB Medium and Agar Plates

Luria-Bertani (LB) medium is a nutritionally rich medium that can be used for the preparation of plasmid DNA and recombinant proteins. It is one of the most common media used for maintaining and cultivating recombinant strains of Escherichia coli.

To 950 ml of deionised water, add:

• Bacto Tryptone – 10 grams
• NaCl – 10 grams
• Yeast extract – 5 grams

Shake until all the solutes have completely dissolved. Adjust the pH to 7.0 with 5N NaOH (≈ 0.2 ml). Adjust the total volume to one litre with deionised water. For LB plates, add 15g/litre of Bacto agar to the medium before autoclaving. Sterilise by autoclaving (standard autoclaving liquid cycle protocol).

Allow to cool down and add the right amount of antibiotic.

Add about 15 – 20 ml of solution to plates in a sterile environment. Allow to settle and store at 4˚C.

Gibson Assembly

Preparation of reagents

Preparation of 6ml of 5X isothermal reaction buffer by combining (This buffer can be aliquoted and stored at –20°C):

• 3 ml of 1M Tris-HCl pH 7.5
• 150 ml of 2M MgCl2
• 60 ml of 100mM dNTP
• 300 ml of 1M DTT
• 1,5 g PEG-8000
• 300 ml of 100mM NAD

One-step isothermal DNA assembly
protocol (Gibson Reaction)

For one reaction containing 40 µl:

• 8 µl 5X isothermal buffer
• 0.8 µl of 0.2 U.µl –1 or 1.0 U.µl –1 T5 exonuclease
• 4 µl of 40 U.µl –1 Taq DNA ligase
• 0.5 µl of 2 U.µl –1 Phusion DNA polymerase.
• 5 µl of DNA
• Water up to 40 µl

50 ºC ----- 1 hour

Notes:

• All isothermal assembly components can be stored at –20°C in a single mixture at 1.33X concentration for more than one year. The enzymes are still active after more than ten freeze-thaw cycles. The aliquots should be kept on ice until ready to use.
• The exonuclease amount is ideal for the assembly of DNA molecules with 20– 150 bp overlaps.
• Between 10 and 100 ng of each 6 kb DNA fragment was added.
• For larger DNA segments, proportional amounts of DNA should be added (for example, 250 ng of each 150 kb DNA segment).

DNA Precipitation

Add 1/10 of sodium acetate (3M, pH 5.2) to the total volume of DNA to be precipitated. Vortex to make sure that the solution is well mixed.

Add 2.5 X total volume in eppendorf of 100% ethanol. Vortex and keep the mixture at -20˚C for 30 minutes.

Centrifuge at maximum speed for 20 minutes.

Discard the supernatant without disturbing the pellet and add about 500 µl of 70% ethanol.

Centrifuge for one minute at maximum speed. Discard the supernatant.

Add about 500 µl of 70% ethanol again. Centrifuge for one minute at maximum speed. Discard the supernatant.

Remove as much ethanol as possible using a glass Pasteur pipette. Allow to air dry.

Resuspend the DNA in 20 µl of deionised sterile water.

Notes:

• Keep the 100% ethanol at -20˚C. The ethanol must always be cold prior to use.
• Centrifugation at 4˚C is preferable.

Preparation of Competent E. coli

Preparation of Reagents

Buffer 1:

 
• 30 mM KOAc, 100 mM RbC12, 10 mM CaCl2, 50 mM MnC12, 15% glycerol, pH 5.8
• For 500 ml: 1.47 g KOAc (MW 98.14) 
• 6.04 g RbC12 (MW 120.92) 
• 0.74 g CaC12 (MW 147.02) 
• 4.94 g MnC12-4H20 (MW 197.9) 
• 75 ml glycerol 
• pH to 5.8 with dilute acetic acid.
• Filter sterilize
• Buffer 2:

10 mM MOPS/KOH pH 6.5, 75 mM CaC12, 10 mM RbC12, 15% glycerol

For 100 ml: 0.21 g MOPS (MW 209.26) 

1.10 g CaC12 (MW 147.02)

 

0.12 g RbC12 (MW 120.92) 

15 ml glycerol 

pH to 6.5 with 1 N KOH.

Filter sterilize.

Protocol

Streak desired E. coli strain on fresh LB plate. Grow overnight at 37°C. 

Inoculate a single colony into 5 ml LB. Grow overnight, shaking at 37° C. 

Inoculate about 1 ml into 200 ml LB in a 2 1 flask. Shake at 37°C until OD550 = 0.5. 

Chill flask in ice-water 5 minutes. 

Spin 5 minutes at 6,000 rpm in GS3 rotor. 

Resuspend pellet in 80 ml ice cold Buffer 1. 

Chill in ice-water 5 minutes. 

Spin 5 minutes at 6,000 rpm in GS3 rotor. 

Resuspend pellet in 8 ml ice cold Buffer 2. 

Chill in ice-water 15 minutes. 

Make 50, 100 and 200 ml aliquots in 1.5 ml Eppendorf tubes.

 

Flash-freeze in liquid nitrogen. 

Store at -80oC.

Notes:

• Keep buffers, tips, tubes, rotors, etc. ice cold