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) bindin g to the inc-control region contained on a 231 bp fragment were invest igated 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, decrease s in jM correlated with CRP binding to both the promoter-proximal and the operator-proximal CRP binding sites. These results show that bindi ng of the CRP:cAMP complex to the operator-proximal CRP binding site i nduces a structural change in lac DNA.