CRP:cAMP complex binding to the lac operator region induces a structural change in lac DNA.

Changes in DNA structure induced by cAMP receptor protein (CRP) binding to the lac-control region contained on a 231 bp fragment were investigated by measurement of the molar cyclization factor (jM). Increases in jM were observed at low to moderate CRP: cAMP complex concentrations and correlated with CRP binding to the promoter-proximal CRP binding site. At CRP:cAMP complex concentrations greater than 200 nM, decreases in jM correlated with CRP binding to both the promoter-proximal and the operator-proximal CRP binding sites. These results show that binding of the CRP:cAMP complex to the operator-proximal CRP binding site induces a structural change in lac DNA.