Synthetic Lysine-Dropout Medium (SD-Lys)

Reagent	Quantity	Final concentration
Difco yeast nitrogen base without amino acids	6.7 g	6.7 g/L
Agar	20 g	20 g/L
Supplements for SD-lys:
l-Leucine (100×)	10 mL	8.4 mg/L
l-Histidine HCl (100×)	10 mL	4.2 mg/L
l-Methionine (100×)	10 mL	4.2 mg/L
Uracil (100×)	10 mL	2.5 mg/L
Dextrose (40%)	50 mL	20 g/L
Combine 10 mL of each of the SD-lys supplements (100× l-leucine, 100× l-histidine HCl, 100× l-methionine, 100× uracil) with 6.7 g of Difco yeast nitrogen base without amino acids and 20 g agar, and add 950 mL of deionized water. Autoclave for 20 min at 15 psi (1.05 kg/cm²). After autoclaving, add 50 mL of a 40% dextrose solution. Cool the medium to ∼60°C and pour into Petri dishes (∼25 mL per 100-mm plate). Store the SD-lys plates at 4°C; they will keep for at least 6 mo. (Note that this recipe is optimized for BY4742 strains. It should be adjusted if another yeast strain is used as a recombination host.)