X-gal

Definition

X-gal is a substrate used in molecular biology to detect the presence of β-galactosidase enzyme activity. It turns blue when cleaved by this enzyme, providing a visual marker for gene expression.

5 Must Know Facts For Your Next Test

1. X-gal is commonly used in blue-white screening to differentiate between recombinant and non-recombinant bacterial colonies.
2. When X-gal is cleaved by β-galactosidase, it produces an insoluble blue product, indicating enzyme activity.
3. It is often used in conjunction with IPTG which induces the expression of genes under control of the lac promoter.
4. X-gal itself is not an inducer of the lac operon; it only acts as a substrate for β-galactosidase.
5. The blue color development indicates that the lacZ gene, which encodes β-galactosidase, is functional.

Review Questions

Related terms

IPTG: A molecular mimic of allolactose that induces the lac operon.

β-Galactosidase: An enzyme that hydrolyzes lactose into glucose and galactose and also cleaves X-gal.

Blue-White Screening: A technique to distinguish between bacteria that have inserted DNA fragments from those that have not.