title: [Polymorphism of the left-handed helix (Z form) of poly(dG-dC).poly(dG-dC) induced by MgCl2, studied by infrared spectroscopy].
abstract: The existence of a left-handed double-helical DNA, called Z-DNA was proved by X-ray crystallographic analysis of the hexanucleotide d(CpGpCpGpCpG). The possible biological relevance of the Z conformation is enhanced by recent studies using immunostaining. Antibodies against Z-DNA have been raised and used to detect the Z conformation in polytene and mammal chromosomes. In this work we have studied the conditions necessary to generate the transition from the right-handed to the left-handed conformation of poly d(G-C).poly d(G-C) exposed to various concentrations of MgCl2 and various relative humidities. The infrared (IR) spectra were used to characterize the different conformations. Only below 0.5 Mg2+ ion per nucleotide we have observed the right-handed helix. Above 1 Mg2+ ion per nucleotide, the left-handed helix is always present under low and high relative humidity conditions. Furthermore, under low relative humidity and high salt content conditions we found a new IR spectrum which can be correlated with a polymorphic Z form, called here Z degree form.
mesh_terms: D004247:DNA / Q000032:analysis; D008274:Magnesium / Q000494:pharmacology*; D015636:Magnesium Chloride; D009690:Nucleic Acid Conformation / Q000187:drug effects*; D011089:Polydeoxyribonucleotides / Q000032:analysis*; D011110:Polymorphism, Genetic; D013055:Spectrophotometry, Infrared; D014961:X-Ray Diffraction
chemical_list: D011089:Polydeoxyribonucleotides; D015636:Magnesium Chloride; C019530:poly(dC-dG); D004247:DNA; D008274:Magnesium
vernacular_title: Polymorphisme de l'hélice gauche (forme Z) du poly(dG-dC).poly(dG-dC) induit par le MgCl2 étudié par spectroscopie infrarouge.