Millimolar concentrations of zinc and other metal cations cause sedimentation of DNA

We demonstrate that DNA sediments in the presence of millimolar concentrations of zinc or related metal cations and that EDTA entirely dissolves the sediment. The sedimentation is promoted by alkaline pH but the pH dependence is abolished by submillimolar concentrations of phosphate anions. We suspect that the metal cations generate sedimenting particles of insoluble hydroxides or phosphates for which DNA has a strong affinity. The events involved in DNA-metal phosphate cc-sedimentation are similar to the processes that enable calcium phosphate-assisted transfection. Hence, work with even submillimolar concentrations of zinc and most other metal cations, which many DNA-binding proteins need for their activities, requires care to avoid the sedimentation of DNA. Literature reporting about zinc effects on DNA is discussed from the point of view of the present results.