TABLE 6.
Activation of wild-type and mutant CodY proteins by individual BCAAsa
| CodY concn (nM) | CodY type | Concn (mM) of effector that gave 50% protection of ilvB site II |
||
|---|---|---|---|---|
| Ile | Val | Leu | ||
| 85 | Wild-type | <2.5 | ||
| F71E | >40 | |||
| R61A | >40 | |||
| 160 | Wild-type | 2.5-5.0 | <5.0 | |
| F71E | >40 | >40 | ||
| R61A | >40 | >40 | ||
| 100 | Wild-type | <2.5 | ||
| F40A | >10 | |||
| 125 | Wild-type | <2.5 | ||
| F98A | >10 | |||
a
DNase I footprinting experiments shown in Fig. 2 to 6 and other experiments (not shown) were analyzed to determine the concentrations of BCAAs that gave 50% protection of the high-affinity CodY binding site II in the ilvB promoter region at the fixed CodY concentrations tested. CodY concentrations were chosen on the basis of titration experiments with wild-type CodY (which varied slightly from day to day and batch to batch) so as to exclude effector-independent binding while permitting detection of BCAA-induced binding. The mutant forms of CodY were tested at the same concentrations as wild-type CodY.