adapted from this protocol.

Material:

1M Lithium Acetate (MW 65.98 g/mol): 10.2 g in 100 mL ddH2O – autoclaved
50% PEG: Dissolve 50g in 30 mL ddH2O and stir, bring total volume up to 100 mL, heat and stir to combine. Filter sterilize (this might take about 10-20 min). Bubbles will disappear once you filter.
ssDNA: Single-stranded salmon sperm carrier DNA. We do not sonicate this DNA. It must be boiled before use, but you can refreeze 3 times after the initial boil (if you keep it on ice at all times) before you need to boil it again. Keep a few tubes in your own box for you personal use.
Petri dishes with solid medium for spreading transformants
95-99% ethanol with flaming glass spreader

Equipment:

microcentrifuge
42℃ water bath
cell spreader or glass rod
containers for ethanol
P1000 pipette
P200 pipette
P20 pipette

Method

Spin down 100 µL frozen competent cells from the –80°C freezer 30 s at ~14,000 rpm or max speed of the microcentrifuge. Use one tube per transformation reaction.
Remove supernatant with a pipette and add the following in order.
- 240 µL 50% PEG
- 36 µL 1M LiAc
- 50 µL ssDNA
- 34 µL DNA + water

Total volume should be 360 µL, It is usually enough to add 1 µL plasmid DNA and 33 µL of water for a normal circular plasmid prepared using a miniprep kit. If you have many similar transformations, A master mix (PEG, LiAc, ssDNA and water) can be made by leaving out your DNA. Such a mix should be vortexed lightly before being added to the cells.

Resuspend the yeast cells in the mixture by vortexing well to remove any clumps.
Heat shock in 42℃ water bath for 45 minutes.
Spin down at 14,000 rpm or max speed for 30 s, remove supernatant with a micropipette.
Add 100 µL of sterile water to the cells, resuspend by pipetting up and down with a P200 pipette and take out 10-20% of the cells to a fresh tube and save these cells in the fridge or on ice. Plate the rest of the cells on appropriate medium. Incubate plates at 30℃ for 2-4 days or until colonies appear (check after two days).