TABLE 3.
β-Galactosidase activities directed by the FF-gal Δ4 promoter in the presence of plasmids expressing NNR and its altered derivatives and FNRa
| Plasmid | β-Galactosidase activity
|
Fold repressionb | |
|---|---|---|---|
| Aerobic growth (LG) | Anaerobic growth (LG + nitrate) | ||
| pNNR | 348 ± 18 | 122 ± 2 | 2.9 |
| pGS24 | 231 ± 5 | 7 ± 1 | 33 |
| pNNR (Y35F) | 347 ± 21 | 142 ± 27 | 2.4 |
| pNNR (F82A) | 248 ± 9 | 220 ± 11 | 1.1 |
| pNNR (F82Y) | 266 ± 63 | 122 ± 17 | 2.2 |
| pNNR (Y93F) | 368 ± 26 | 111 ± 7 | 3.3 |
| pNNR (S96T) | 413 ± 67 | 67 ± 11 | 6.2 |
| pNNR (C103S) | 281 ± 6 | 93 ± 9 | 3.0 |
a
Activities were measured in duplicate on at least three independently grown cultures; standard errors are shown. Cultures were grown anaerobically in LG, to which was added 50 mM nitrate, as indicated. E. coli JRG1728(pRW50/FFgal Δ4) was transformed with plasmids expressing NNR (pNNR), its derivatives expressing altered NNR proteins, as indicated, and FNR (pGS24). Units of β-galactosidase activity are as defined by Miller (15).
b
The fold repression is the ratio of activities in cultures grown aerobically in LG to the activities in cultures grown anaerobically in LG plus SNP.