M-DNA: A complex between divalent metal ions and DNA which behaves as a molecular wire.

M-DNA is a complex of DNA with divalent metal ions (Zn(2+), Co(2+), or Ni(2+)) which forms at pH conditions above 8. Upon addition of these metal ions to B-DNA at pH 8.5, the pH decreases such that one proton is released per base-pair per metal ion. Together with previous NMR data, this result demonstrated that the imino proton in each base-pair of the duplex was substituted by a metal ion and that M-DNA might possess unusual conductive properties. Duplexes of 20 base-pairs were constructed with fluorescein (donor) at one end and rhodamine (acceptor) at the other. Upon formation of M-DNA (with Zn(2+)) the fluorescence of the donor was 95 % quenched. Fluorescence lifetime measurements showed the presence of a very fast component in the decay kinetics with tau</=10 ps. The fast component was absent in B-DNA and in M-DNA lacking an acceptor chromophore; a result which is only consistent with electron transfer. Efficient signal transduction was also observed between the two fluorophores separated by 54 base-pairs (over 150 A) in an M-DNA duplex. The addition of a sequence-specific DNA-binding protein prevented the flow of electrons and this was reversed by protease digestion. Therefore, M-DNA behaves as a molecular wire and could be manipulated to prepare self-assembling electronic circuits. Copyright 1999 Academic Press.