Table 2.
Lactose Analogs Used in DNA Cloning Technology
| Galactoside | Stock concentrationa |
Use | Characteristics | Reference |
|---|---|---|---|---|
| Isopropyl-1-thio-β-d-galactoside (IPTG) | 100 mM | Very effective inducer | Nonmetabolizable inducer | Barkley and Bourgeois, 1978 (pp. 177-220) |
| 5-Bromo-4-chloro-3-indolyl-β-d - galactoside (Xgal) | 20 mg/ml (dissolved in N,N dimethyl formamide) | Identification of lacZ+ bacteria, especially useful for detecting β-galactosidase made by recombinant vectors | Noninducing chromogenic substrate of β-galactosidase (cleavage of Xgal results in blue color); production of blue color independent of lacY gene product | Miller, 1972 |
| Orthonitrophenyl- β-d -galactoside (ONPG) | 10 mM | β-galactosidase assays | Chromogenic substrate of β-galactosidase (cleavage of ONPG results in yellow color) | Miller, 1972 (pp. 352-355) |
| 6-O-β-d-Galacto-pyranosyl d -glucose (allolactose) | Inducer of the lactose operon in vivo; lactose is converted into allolactose by β-galactosidase | Zabin and Fowler, 1978 (pp. 89-121) | ||
| Phenyl-β-d-galacto-side (Pgal) | 2 mg/ml | Selection for lac constitutive mutants | Noninducing substrate of β-galactosidase; uptake partly dependent on lacY gene product | Miller, 1978 (pp. 31-88) |
| Orthonitrophenyl- β-d -thiogalacto- side (TONPG) | 10 mM | Selection for lac− mutants | Transported into cells by lac permease (the lacY gene product); inhibits cell growth at high concentration | Miller, 1978 (pp. 31-88) |
a
Stock solutions should be dissolved in sterile water unless otherwise noted.