title: Z* DNA, the left-handed helical form of poly[d(G-C)] in MgCl2-ethanol, is biologically active.
abstract: The interconversion between the right (R) and left (L) helical forms of poly[d(G-C)] occurs at low concentrations of MgCl2 and EtOH, acting together in a highly synergistic manner. Thus, the cooperative R---L transition is induced by only 0.4 mM and 4 MM MgCl2 in combination with 20% and 10% EtOH, respectively. The L form of poly[d(G-C)] formed under these conditions has the spectroscopic properties (absorption, circular dichroism) previously demonstrated under high salt conditions (Pohl and Jovin, 1972) and thought to correspond to the left-handed Z DNA structures recently established by X-ray crystallography (Wang et al., 1979; Drew et al., 1980). However, L DNA formed in Mg2+-EtOH (which we designate as Z* DNA) has unique properties: a) it can be sedimented readily out of solution at low speed, indicative of condensation and intermolecular aggregation; b) it supports the binding of several intercalating (ethidium bromide, actinomycin D) and non-intercalating (mithramycin) drugs, although these interact preferentially with the R (i.e., B) form of DNA; and c) it functions as a template for Escherichia coli RNA polymerase. B and Z* DNAs can be generated under identical ionic conditions and compared in a number of biochemical systems. Our results suggest that left-handed DNA may form under physiological conditions and serve a biological function.
mesh_terms: D003461:Crystallography; D004247:DNA / Q000378:metabolism*; D003609:Dactinomycin / Q000378:metabolism; D004214:Distamycins / Q000378:metabolism; D000431:Ethanol; D004996:Ethidium / Q000378:metabolism; D008274:Magnesium; D015636:Magnesium Chloride; D008926:Plicamycin / Q000378:metabolism; D011089:Polydeoxyribonucleotides; D012996:Solutions; D014965:X-Rays
chemical_list: D004214:Distamycins; D011089:Polydeoxyribonucleotides; D012996:Solutions; D015636:Magnesium Chloride; D003609:Dactinomycin; C019530:poly(dC-dG); D000431:Ethanol; C030000:stallimycin; D004247:DNA; D004996:Ethidium; D008274:Magnesium; D008926:Plicamycin