Characterization of a zinc blotting technique: Evidence that a retroviral gag protein binds zinc

We have characterized a simple method that uses ⁶⁵ZnCl₂ to detect zinc-binding proteins that have been immobilized on nitrocellulose. Conditions have been identified that permit the detection of as little as 1 μg of some zinc-binding proteins. The specificity of the binding is indicated by the ability of other divalent metal ions to compete with ⁶⁵ Zn(II) in this assay. We have used this technique to provide evidence that the nucleic acid-binding gag protein of retroviruses also binds zinc. This technique can be applied to biological mixtures of proteins and may be used in proteolytic mapping studies to identify protein fragments that have zinc-binding activity.