X-Gal

X-gal (also known as 5-bromo-4-chloro-3-indolyl-?-D-galactoside) is soluble in either DMSO or DMF, and can be stored in solution in the freezer for up to 6 months. Protect the solution from light.

To add X-gal to previously made agar plates, pipette 40 ?l of a 40 mg/ml stock solution onto a 100mm pre-poured agar plate and spread evenly with a sterile spreader. Let dry 15 minutes and store plates away from light.

IPTG can be reconstituted in water. Make a stock of 100 mM in water and store working aliquots at -20°C. X-gal can be reconstituted in DMSO, or in a 50:50 mix of DMSO and water. To do the latter, you must dissolve in DMSO first, and then add water to bring up to final volume. It is not necessary to filter sterilize these solutions.

The X-gal solution should be protected from light. To make plates, add 50 ug/ml X-gal and 1 mM (0.24 mg/mL) IPTG to LB/agar that has been cooled down to 50°C. To spread on top of plates, use 50 µl 2% stock of X-gal and 30 µl 100 mM stock of IPTG. 

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