Magnesium reduces nickel inhibition of DNA polymerization.

The activities of DNA polymerization and DNA ligation in extract of Chinese hamster ovary cells were both stimulated by MgCl2. DNA polymerization was stimulated by MgCl2 above 0.25 mM, whereas, MgCl2 above 2 mM was required to stimulate DNA ligation. The activity of DNA polymerization maintained a plateau at MgCl2 1-12 mM, whereas DNA ligation reached a maximal activity at MgCl2 6 mM and decreased thereafter. NiCl2 0.1-0.2 mM also had a stimulatory effect on DNA polymerization, but was much less potent than MgCl2. However, nickel ion (Ni2+) had no detectable stimulating effect on the activity of DNA ligation. In the presence of MgCl2, the activities of DNA polymerization and DNA ligation decreased with increasing concentration of NiCl2. Ni2+ inhibition of DNA polymerization was reduced by increasing the concentration of MgCl2, but increasing the concentration of MgCl2 did not reduce Ni2+ inhibition of DNA ligation. Preincubating cell extract with MgCl2 decreased the Ni2+ inhibition of DNA polymerization but not DNA ligation. These results suggest that Ni2+ may compete with magnesium ion (Mg2+) to reduce DNA polymerization, but this mechanism seems not applicable to Ni2+ inhibition of DNA ligation.