Specific interaction with guanine residues of Z-form DNA by bleomycin-nickel(III) complex

The Ni(III) complex of bleomycin (BLM) reacts with guanine residues of the oligomer duplex only under high salt condition (4.5 M NaCl) where the (dC-dG)6 sequence exists as the isolated Z-form segment. In addition, the (dC-dG)n inserts were subcloned into a plasmid so that reactivity of the BLM-Ni(III) complex with restriction fragments could be examined. Results are reported for two fragments: an EcoRI-DdeI fragment in which the (dC-dG)n insert is flanked at the 5' end by a segment of B-DNA and a HindIII-DdeI fragment in which the (dC-dG)n fragment is embedded at both ends by stable B-DNA forming segments. The BLM-Ni(III) complex does not bind to (dC-dG)5 sequence of pBRZ10 DNA fragment under any conditions, but to several guanine residues of (dC-dG)8 and (dC-dG)12 sequences of pBRZ16 and pBRZ24 DNA fragments in 4.5 M NaCl solution. In the fragments of pBRZ16 and pBRZ24 DNAs, the BLM-Ni(III) complex reacts with most of guanine bases of (dC-dG)8 and (dC-dG)12.