FIG. 2.

DNase I footprints of TyrR bound to the promoter regions of tpl or tpl-mut1. The DNA fragments were generated by EcoRI-PstI digestion of pUC19-tpl (lanes 2 to 7, both panels), or pUC19-tplmut1 (lanes 8 and 9, both panels). The latter construct contains a G-to-A change in box A. Both fragments were labeled with ³²P at the 5′ ends as described in Materials and Methods. Treatment with DNase I was carried out in the presence (lanes 3 to 9, both gels) or absence (lanes 2, both gels) of TyrR. All reaction mixtures contained 0.2 mM l-tyrosine, 0.2 mM ATP, and 0.7 nM DNA. The concentrations of TyrR used were as follows: lanes 3, 5 nM; lanes 4, 10 nM; lanes 5 and 8, 20 nM; lanes 6, 40 nM; lanes 7 and 9, 80 nM. Lanes 1 contain the A+G sequence of tpl DNA. The regions protected by TyrR are indicated. Box A is shown in the left gel, and boxes B and C are shown in the right gel. Each of the DNA sequences shown reads from the 5′ end (bottom) toward the 3′ end (top) as shown in Fig. 1.