FIG. 4.

DNA binding of mutant XylS(3L) to wild-type Pm promoter. EMSA for binding of ³²P-labeled wild-type Pm DNA fragment in the presence (+) or absence (−) of 3MB by purified extracts containing mutant XylS(3L) protein. Mobility shift assays were performed as described in Materials and Methods with either no protein added (first and fifth lanes from the left) or increasing amounts (0.5, 1, and 10 μg) of extracts that contained XylS(3L) (second to fourth lane and sixth to eighth lane). Controls with an excess of nonlabeled Pm DNA strongly reduced the amount of shifted DNA, while the addition of excess unspecific DNA did not modify the shift.