Abstract:
:Blue/white selection is the standard method for detecting a cloned DNA fragment. In the absence of an insert, uninterrupted expression of the vector-encoded alpha-complement of beta-galactosidase (beta-gal), results in the hydrolysis of X-gal (5-bromo-4-chloro-3-indolyl-beta-D-galactoside) and the subsequent blue staining of the host colony or bacteriophage plaque expressing the carboxyterminal portion of the beta-gal gene (lacZ). A white or clear colony or plaque indicates the presence of an insert. Because of its water insolubility, X-gal is dissolved in hazardous solvents such as dimethylformamide and then added to the medium following autoclaving. X-gal can be spread on previously plated medium, but this may result in an uneven color development. Also, incubation at 4 degrees C is frequently required for the distinction between a positive recombinant (unstained colony or plaque) and a stained negative. S-Gal (3,4-cyclohexenoesculetin-beta-D-galactopyranoside), a novel beta-gal substrate, is autoclavable and microwavable, allowing for dry-blending of the dye directly into the medium. Black S-Gal-stained colonies are visibly distinguishable from unstained colonies at an earlier time than X-gal. In addition, detection of the unstained signal over background is enhanced by 25% using S-Gal-containing medium, compared to medium containing X-gal. These characteristics offer convenience and better suitability for automated colony or plaque analyses.
journal_name
Biotechniquesjournal_title
BioTechniquesauthors
Heuermann K,Cosgrove Jdoi
10.2144/01305pf01subject
Has Abstractpub_date
2001-05-01 00:00:00pages
1142-7issue
5eissn
0736-6205issn
1940-9818journal_volume
30pub_type
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