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X-Gal is the common short name for 5-bromo-4-chloro-3-indolyl-β-D-galactopyranoside. It is a substrate for beta-galactosidase (lacZ) and turns blue upon being cleaved. It is commonly used for blue-white screening or detection of LacZ transgenes in cells and tissues.

A stock solution of X-gal is commonly made with 20 mg/ml X-gal in DMF (dimethylformamide). When pouring agar plates, a typical final concentration is 20 μg/ml. Note that DMF is toxic. Take care when preparing X-Gal solution. Protect X-Gal from light to prevent degradation.

Protocols using X-Gal


  • Also may make stock solution with 50 mg in about 250 µl DMSO

See also

External links

  • S-Gal - a variation of X-Gal [1]