title: Fluorescence-detected circular dichroism of ethidium bound to poly(dG-dC) and poly(dG-m5dC) under B- and Z-form conditions.
abstract: The equilibrium binding of ethidium to poly(dG-dC) and poly(dG-m5dC) under conditions favoring B and Z forms was investigated with fluorescence-detected circular dichroism (FDCD) and optical titration methods. FDCD spectra indicate a similar geometry for the intercalated ethidium under both B- and Z-form conditions, even at low levels of bound ethidium. The magnitude of the 310-330-nm FDCD band as a function of the bound drug to base pair ratio (r) indicates ethidium binds to poly(dG-dC) in 4.4 M NaCl and to poly(dG-m5dC) in 25 mM MgCl2 by clustering. Under these conditions, circular dichroism spectra indicate the polymer is largely Z form. Thus, it appears ethidium clusters into regions it has induced into a right-handed form. For all conditions studied, the FDCD spectra provided no evidence for a left-handed binding site. Under B-form conditions, binding is random.
mesh_terms: D055598:Chemical Phenomena; D002621:Chemistry; D002942:Circular Dichroism / Q000379:methods; D004996:Ethidium; D009690:Nucleic Acid Conformation; D011089:Polydeoxyribonucleotides; D013050:Spectrometry, Fluorescence / Q000379:methods; D013329:Structure-Activity Relationship
chemical_list: D011089:Polydeoxyribonucleotides; C019530:poly(dC-dG); C029988:poly(dG-m(5)dC).poly(dG-m(5)dC); D004996:Ethidium