Nickel and cobalt reagents promote selective oxidation of Z-DNA

The structural characteristics of Z-DNA were used to challenge the selectiv ity of guanine oxidation promoted by nickel and cobalt reagents. Base pairi ng and stacking within all helical structures studied previously had hinder ed access to guanine and limited its reaction. However, the Z-helix uniquel y retains high exposure of guanine N7. This exposure was sufficient to dire ct oxidation specifically to a plasmid insert -(CG)(13)AATT(CG)(13)- that a dopted a Z-conformation under native supercoiling. An alternative insert -( CG)(7)- retained its B-conformation and demonstrated the expected lack of r eactivity. For a nickel salen complex made from a particularly bulky ligand , preferential reaction shifted to the junctions within the Z-DNA insert as is common for large reagents. Inactivation of the nickel reagents by high- salt concentrations prevented parallel investigations of Z-DNA, formed by o ligonucleotides. However, the activity of Co2+ was minimally affected by sa lt and consequently confirmed the high reactivity of 5'-p(CG)(4) in its Z-c onformation. These reagents may now be applied to a broad array of targets, since their structural specificity remains predictable for both complex an d helical assemblies of nucleic acids.