EFFECTS OF NICKEL IONS ON POLYMERASE-ACTIVITY AND FIDELITY DURING DNA-REPLICATION IN-VITRO

Nickel is a genotoxic carcinogen. However, the mechanisms of nickel-in duced genotoxicity are not well understood. We have investigated the e ffects of Ni2+ ions on DNA polymerase activity and the fidelity of DNA replication in vitro. The effect of Ni2+ on different DNA polymerases is quite variable. The amount of enzyme inhibition and degree of alte ration in replication fidelity induced by Ni2+ are dependent both on t he polymerase and its associated 3'-5' exonuclease activity. Some poly merases, such as E. coli DNA polymerase I, AMV reverse transcriptase a nd human DNA polymerase alpha, can utilize Ni2+ as a weak substitute f or Mg2+ during DNA replication. Other polymerases are very sensitive t o inhibition by Ni2+ and the IC50 can vary by an order of magnitude. T 4 polymerase is relatively insensitive to inhibition by Ni2+, although the sensitivity is enhanced in the absence of added Mg2+, and Ni pref erentially inhibits the 3'-5' exonuclease function of T7 DNA polymeras e. The fidelity and processivity of DNA polymerases may be either incr eased or decreased by Ni ions in a polymerase dependent manner. The in hibition DNA polymerase activity and altered replication fidelity may contribute significantly to Ni-induced mutagenesis and genotoxicity in vivo.