THE STIMULATORY EFFECT OF NICKEL CHLORIDE ON DNA-REPLICATION IN HUMAN HELA-CELLS AND ESCHERICHIA-COLI

An investigation was undertaken to study DNA replication in cultured human HeLa cells and Escherichia coli in response to nickel chloride (NiCl2). Treatment with NiCl2 increased both the rate of DNA replication and total cell number in HeLa cells and E.coli in a time- and concentration-dependent manner. The maximum stimulation of thymidine uptake into DNA was observed with 0.125-0.25 mM NiCl2 for both cell types. In studies of DNA replication using a crude HeLa cellular extract, NiCl2 at concentrations below 0.125 mM also induced a stimulation over the background of MgCl2-dependent [H-3]dTMP incorporation into activated calf thymus DNA. However, a similar stimulatory effect from NiCl2 was not observed with either purified HeLa DNA polymerase alpha or E.coli DNA polymerase I Klenow fragment. In the absence of Mg2+, the low response of either DNA polymerase alpha or Klenow fragment to stimulation by Ni2+ was thought to be enhanced by the presence of Ni2+-binding proteins presented in the crude HeLa cell extract.