INTERACTION OF ZINC(II) IONS WITH ANTIPARALLEL-STRANDED D(GA)(N) DNA HOMODUPLEXES

In the presence of specific metal-ions (namely zinc but also cadmium, cobalt and manganese), d(GA.TC)(n) DNA sequences can form non-B-DNA co nformations. At low metal-ion concentration they form [GA(GA.TC)] intr amolecular triplexes but, upon increasing the metal concentration, the formation of (GA.GA) intramolecular hairpins is detected. In this pap er we address the question of the specific effects of zinc on the stru cture of the d(GA.TC)(n) sequences. In the presence of zinc, the DMS-r eactivity of the (GA.GA) hairpins is strongly reduced suggesting a dir ect interaction of the metal-ion with the N7-group of the guanines. Th is effect is specific for antiparallel-stranded d(GA)(n) homoduplexes. No such strong decrease in DMS-reactivity is observed in B-DNA duplex es or in d(GGA)(n) and d(GGGA)(n) homoduplexes. In addition, the therm al stability of antiparallel-stranded d(GA)(n) homoduplexes increases in the presence of zinc. On the contrary, the melting temperature of s imilar B-DNA molecules decreases upon increasing the zinc concentratio n. Altogether, these result indicate that zinc plays an specific role on the stabilization of the (GA.GA) intramolecular hairpins.