FIG. 4.

Requirement for cAMP in DNase I footprinting of tpl promoter DNA by CRP. The DNA fragment used in lanes 1 to 5 was an EcoRI-PstI fragment from pUC19-tpl. The fragment used in lanes 6 to 8 was an EcoRI-PstI fragment from pUC19-tplmut1 which contains a critical G-to-A change in box A. Each DNA fragment was labeled with ³²P at the 5′ end. The concentrations of CRP and cAMP are shown at the bottom. The segments protected by CRP are indicated to the right. A+G standards are in the leftmost lane. TyrR (50 nM), l-tyrosine (0.2 mM), and ATP (0.2 mM) were present in each tube.