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

We demonstrate that DNA sediments in the presence of millimolar concentrati ons of zinc or related metal cations and that EDTA entirely dissolves the s ediment. The sedimentation is promoted by alkaline pH but the pH dependence is abolished by submillimolar concentrations of phosphate anions. We suspe ct that the metal cations generate sedimenting particles of insoluble hydro xides or phosphates for which DNA has a strong affinity. The events involve d in DNA-metal phosphate cc-sedimentation are similar to the processes that enable calcium phosphate-assisted transfection. Hence, work with even subm illimolar concentrations of zinc and most other metal cations, which many D NA-binding proteins need for their activities, requires care to avoid the s edimentation of DNA. Literature reporting about zinc effects on DNA is disc ussed from the point of view of the present results.