FIG. 4.

Interaction of Lrp with the promoter region of dadAB from K. aerogenes. pCB888 was digested and radiolabeled as described in Materials and Methods; 0.1 μg of DNA was incubated with increasing amounts of Lrp (lanes 1, 6, and 11, no Lrp; lanes 2, 7, and 12, 8 nM; lanes 3, 8, and 13, 23 nM; lanes 4, 9, and 14, 68 nM; lanes 5, 10, 15, 200 nM) and incubated for 20 min at room temperature; 30 mM l-leucine (lanes 6 to 10) or 30 mM l-alanine (lanes 11 to 15) was added prior to the addition of Lrp. Separation of the bound and unbound fragments by electrophoresis and visualization of the DNA fragments by autoradiography are described in Materials and Methods. The vector and unbound dad promoter bands are indicated by labeled arrows; the two unlabeled arrows indicate the Lrp-dadAp complexes. The unlabeled band that appears in lanes 5, 10, and 15 is most likely the result of an Lrp-vector DNA complex due to the high levels of Lrp present.