TABLE 4.
Site-directed mutagenesis of the xsa and abnA promoters
| Promoter fusion and strain (base substitution) | β-Galactosidase activity (Miller units)a
|
Repression factorb
|
|||
|---|---|---|---|---|---|
| −Ara | +Ara | +Arab | Ara | Arab | |
| xsa′-lacZ | |||||
| IQB405 (wild type) | 7.5 ± 0.2 | 177.3 ± 3.9 | 21.8 ± 0.7 | 23.7 | 2.9 |
| IQB465 (ORX2-27 G→T) | 728.6 ± 67.6 | 580.3 ± 49.5 | 740.1 ± 102.1 | 0.8 | 1.0 |
| abnA′-lacZ | |||||
| IQB410 (wild type) | 3.2 ± 0.7 | 10.0 ± 0.8 | 15.2 ± 2.1 | 3.1 | 4.7 |
| IQB464 (ORB1-38 G→T) | 63.7 ± 5.3 | 27.1 ± 3.3 | 73.2 ± 3.6 | 0.4 | 1.1 |
a
The strains containing different promoter-lacZ fusions were grown on C minimal medium supplemented with casein hydrolysate in the absence of sugar (−Ara), in the presence of arabinose (+Ara), or in the presence of arabinan (+Arab). Samples were analyzed 2 h (t2) after the addition of sugars. The levels of accumulated β-galactosidase activity represent the average of results from three independent experiments.
b
AraR repression was calculated as the ratio of the level of expression (Miller units) obtained in the presence of arabinose (+Ara) or arabinan (+Arab) to the value determined in the absence of sugar (−Ara).