TABLE 2.
Effect of 5′ stem-loop mutations on trp operon expression
| Strain | Relevant genotype | Sequence and/or structural changea | β-Gal activityb
|
β-Gal ratio (−Trp/+Trp) | |
|---|---|---|---|---|---|
| +Trp | −Trp | ||||
| PLBS44 | Wild type | Wild type | 0.2 ± 0.1 | 28 ± 4.3 | 140 |
| PLBS104 | Δ5′S-L | Deletion | 44 ± 2.4 | 371 ± 49 | 8.4 |
| PLBS251 | ΔmtrB | Wild type | 509 ± 52 | 407 ± 32 | 0.8 |
| PLBS252 | Δ5′S-L ΔmtrB | Deletion | 1,110 ± 235 | 1,150 ± 317 | 1.0 |
| PLBS258 | T5A | Structure | 8 ± 2.7 | 178 ± 37 | 22 |
| PLBS259 | G7A | Sequence | 31 ± 6.4 | 350 ± 19 | 11 |
| PLBS260 | C13G | Structure | 13 ± 1 | 334 ± 84 | 26 |
| PLBS262 | A19T | Sequence | 0.9 ± 0.2 | 70 ± 9 | 78 |
| PLBS264 | G24C | Structure | 5 ± 1 | 69 ± 22 | 14 |
| PLBS257 | C3G | Structure | 22 ± 4.3 | 348 ± 76 | 16 |
| PLBS265 | G31C | Structure | 12 ± 2.5 | 260 ± 37 | 22 |
| PLBS266 | C3G G31C | Compensatoryc | 2.9 ± 1.2 | 261 ± 20 | 90 |
| PLBS261 | C15G | Structure | 111 ± 30 | 340 ± 2.3 | 3.1 |
| PLBS263 | G22C | Structure | 100 ± 16 | 376 ± 9.2 | 3.8 |
| PLBS267 | C15G G22C | Compensatory | 2.0 ± 0.7 | 237 ± 9.3 | 119 |
a
The mutation in the 5′ stem-loop alters either the sequence alone or both the sequence and the predicted secondary structure.
b
The β-Galactosidase (β-Gal) activity expressed from the trpE′-′lacZ fusion is given in Miller units (28). Values are the averages from at least four independent experiments ± standard deviations. +, in the presence of; −, in the absence of.
c
Double mutations that are predicted to restore the secondary structure of the 5′ stem-loop.