Description
X-Gal (5-Bromo-4-chloro-3-indolyl-β-D-galactopyranoside) is a high-purity chromogenic substrate. Most commonly used for blue/white screening in E. coli, X-Gal enables precise identification of recombinant colonies through lacZα-complementation, a method first established using M13 cloning vectors.
Its robust chromogenic reaction produces a vivid blue precipitate upon cleavage by β-galactosidase, making it essential for researchers conducting plasmid cloning, promoter characterization, or protein interaction studies.
GoldBio's ≥99% pure X-Gal offers consistent performance across in vivo, in vitro, and fixed-tissue applications. Whether you're building a library, mapping gene expression, or tracing lineages in model organisms, X-Gal remains the gold-standard solution for visible, reliable lacZ reporting.
Many other applications also use X-Gal as a substrate to detect β-galactosidase activity. These include β-galactosidase -antibody linked immunoassays and immunohistochemistry, coliphage detection based on β-galactosidase induction and the detection of micrometastasis formation during tumor progression.
X-gal is commonly used in conjunction with IPTG (GoldBio #I2481) for blue-white screening.
Common Research Applications
(Click each for more information)
Blue/White Screening in Molecular Cloning
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Purpose: To distinguish recombinant from non-recombinant bacterial colonies using lacZα-complementation.
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How It Works: X-Gal (5-Bromo-4-chloro-3-indolyl-β-D-galactopyranoside) is cleaved by β-galactosidase expressed from the lacZα gene fragment. Functional β-galactosidase activity results in blue colonies, while insertional inactivation of lacZα yields white colonies, enabling rapid screening of transformed E. coli for recombinant clones.
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Applications: Plasmid-based cloning workflows with M13 or pUC vectors.
Messing, J., & Vieira, J. (1982). A new pair of M13 vectors for selecting either DNA strand of double-digest restriction fragments. Gene, 19(3), 269–276.
Reporter Gene Assays in Transgenic Models
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Purpose: To monitor spatial and temporal gene expression using lacZ as a transcriptional reporter.
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How It Works: Transgenic organisms engineered with a lacZ reporter gene express β-galactosidase in specific tissues. X-Gal staining yields a blue precipitate, allowing visual localization of gene activity.
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Applications: Mouse and Drosophila models for developmental biology, lineage tracing, and tissue-specific expression analysis.
Sanes, J. R., Rubenstein, J. L., & Nicolas, J. F. (1986). Use of a recombinant retrovirus to study post-implantation cell lineage in mouse embryos. The EMBO Journal, 5(12), 3133–3142.
Characterization of Promoter Activity
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Purpose: To evaluate the strength, regulation, and specificity of promoters using lacZ as a reporter.
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How It Works: The lacZ gene is placed downstream of a promoter of interest. β-galactosidase expression is measured via X-Gal staining or Miller assay, correlating with promoter activity.
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Applications: Promoter mapping in bacterial and eukaryotic systems using lacZ fusion constructs.
Simons, R. W., Houman, F., & Kleckner, N. (1987). Improved single and multicopy lac-based cloning vectors for protein and operon fusions. Gene, 53(1), 85–96.
Histochemical Staining in Fixed or Whole-Mount Tissues
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Purpose: To localize β-galactosidase expression in cells and tissues after fixation.
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How It Works: X-Gal serves as a substrate in fixed tissue preparations; enzymatic cleavage by β-galactosidase yields an insoluble blue precipitate, allowing visual identification of reporter expression in situ.
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Applications: Developmental biology and neuroscience studies tracing gene expression patterns in embryos or organs.
Lobe, C. G., et al. (1999). Z/AP, a double reporter for cre-mediated recombination. Developmental Biology, 208(2), 281–292.
Protein-Protein Interaction Studies Using lacZ Reporters (e.g., Two-Hybrid Systems)
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Purpose: To detect molecular interactions via reconstitution of transcriptional activity leading to lacZ expression.
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How It Works: In bacterial two-hybrid assays, bait and prey proteins reconstitute a signal transduction pathway that activates lacZ expression. X-Gal provides a chromogenic readout for successful interactions.
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Applications: Bacterial systems for mapping protein interaction networks.
Karimova, G., Pidoux, J., Ullmann, A., & Ladant, D. (1998). A bacterial two-hybrid system based on a reconstituted signal transduction pathway. Proceedings of the National Academy of Sciences, 95(10), 5752–5756.
Benefits:
- Enables reliable blue/white colony screening: X-Gal provides visual, high-contrast differentiation between recombinant and non-recombinant E. coli colonies, an essential step in molecular cloning workflows.
- Historically validated in foundational cloning vectors: Used in M13 and pUC systems since the 1980s, X-Gal remains the industry-standard chromogenic substrate for lacZ-based selection.
- Supports broad genetic applications: Beyond cloning, X-Gal is crucial in promoter assays, lineage tracing, and bacterial/two-hybrid interaction systems.
- Compatible with both in vivo and fixed-tissue systems: Allows for staining of live colonies or lacZ expression in fixed tissue sections or whole-mount organisms.
- Minimizes background noise: High specificity for β-galactosidase ensures low false-positive rates in lacZ reporter detection.
Storage/Handling
Store at -20°C. Protect from Light.
X-Gal Quick Answers
X-gal is the chromogenic substrate for the enzyme β-galactosidase. When X-gal is cleaved by
β-galactosidase, it forms galactose and 5-bromo-4-chloro-3-hydroxyindole.
5-bromo-4-chloro-3-hydroxyindole can dimerize and then is oxidized, forming 5,5'-dibromo-4,4'-dichloro-indigo, an insoluble blue product.
The blue product suggests the presence of β-galactosidase. Therefore, this substrate is often used as a reporter in molecular biology.
Instructions to prepare a 20 mg/ml X-gal stock solution are as follows
1. Weigh 200 mg of X-Gal into a 15 ml polypropylene centrifuge tube.
2. Add 10 mL of Dimethylformamide (DMF). Vortex to dissolve the X-Gal.
3. Store at -20°C. Wrap the centrifuge tube in aluminum foil to protect from light.
Note: The X-Gal solution is stable for 6-12 months unless improperly handled. We recommend making 1 ml aliquot portions of the solution to minimize degradation if there will be frequent small scale use of the X-Gal solution.
For blue-white screening, use 10 µl per 1 mL of media if you’re using a 20 mg/ml stock solution. If you’re using a 100 mg/ml stock solution, which is only stable for 1 week, use 2 µl.
- Store powder X-gal at -20°C. Protect from Light.
- Store X-gal stock solution at -20°C. It’s important to protect your stored stock solution from light. You can do this by wrapping the tube in aluminum foil.
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