title: CAP binding to B and Z forms of DNA.
abstract: We have examined the interaction between the cyclic AMP receptor protein (CAP) and a small DNA fragment containing its specific recognition sequence by circular dichroism spectroscopy. The binding of CAP to this fragment induces a B to "C-like" change in the CD spectrum, which is different from that observed for non-specific binding. A one-to-one (CAP dimer to DNA) binding stoichiometry was deduced from spectroscopic titration data, as was a non-specific binding site size of 17 bp/dimer. In addition, we have compared the non-specific binding affinity of CAP for the B and Z forms of synthetic DNA copolymers. A slight preference for the B form was found. These results do not support the recent specific suggestion that CAP binds to a left-handed form of DNA (1), but indicate more generally that an optically detectable conformational change takes place in DNA on binding CAP.
mesh_terms: D001482:Base Composition; D002876:Chromosomes, Bacterial; D002942:Circular Dichroism; D004247:DNA; D004269:DNA, Bacterial / Q000235:genetics; D004926:Escherichia coli / Q000235:genetics; D009690:Nucleic Acid Conformation; D011485:Protein Binding; D011487:Protein Conformation; D011953:Receptors, Cyclic AMP / Q000235:genetics*
chemical_list: D004269:DNA, Bacterial; D011953:Receptors, Cyclic AMP; D004247:DNA