Specific cleavage of DNA at CG sites by Co(III) and Ni(II) desferal complexes.

In recent years, there has been growing interest in interaction of metal complexes with nucleic acids and in particular for their ability to cleave DNA [1-5]. Some important nucleolytes are Ctt(lI)-OP [2], Fe(I1)-BLM [3], Fe(II)-EDTA [4], metalloporphyrins [5], Cu arid Co complexes of substituted phenanthrolines [6] and Ni(ll) complexes of azamacrocycles [7] and a tripeptide GlyGly-His [18]. These reagents cleave DNA either by oxidative degradation of deoxyribose moiety or by base modification, leading ultimately to strand scission. We have recently shown [9] that Cu(ll) 1, Co(Ill) 2 and Ni(II) 3 complexes of a sideroplaore chelating drug desferal cleave plasmid DNA, in contrast to the corresponding Fe(II) complex which is inert in DNA scission reaction. In this paper, by employing synthetic oligonucleotides, we demonstrate that while the Cu(II) complex of desferal has only rnarginal sequence preference for cleavage reactions (CG > AT), Co and Ni complexes cleave DNA only at CG sites and are inef/~etive at AT sites.