FIG. 3.

DNase I footprints of CRP bound to the tpl promoter region. The DNA fragment used was generated by EcoRI-PstI digestion of pUC19-tpl and labeled with ³²P at the 5′ end. The DNA was treated with DNase I in the presence (lanes 3 to 7) or absence (lane 2) of CRP and cAMP. The concentrations of DNA and cAMP were 1 nM and 100 μM, respectively. The concentrations of CRP were as follows: lane 3, 10 nM; lane 4, 25 nM; lane 5, 50 nM; lane 6, 75 nM; lane 7, 100 nM. Lane 1 contains the A+G sequence of the DNA. Segments protected by CRP are indicated to the right. The sequences read from the 5′ end (bottom) toward the 3′ end (top) as shown in Fig. 1.